Mortality in meningococcal infections

Global Case Fatality of Bacterial Meningitis During an 80-Year Period: A Systematic Review and Meta-Analysis

Importance

The impact of vaccination, antibiotics, and anti-inflammatory treatment on pathogen distribution and outcome of bacterial meningitis over the past century is uncertain.

Objective

To describe worldwide pathogen distribution and case fatality ratios of community-acquired bacterial meningitis.

Data Sources

Google Scholar and MEDLINE were searched in January 2022 using the search terms bacterial meningitis and mortality.

Study Selection

Included studies reported at least 10 patients with bacterial meningitis and survival status. Studies that selected participants by a specific risk factor, had a mean observation period before 1940, or had more than 10% of patients with health care-associated meningitis, tuberculous meningitis, or missing outcome were excluded.

Data Extraction and Synthesis

Data were extracted by 1 author and verified by a second author. The study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. Random-effects models stratified by age (ie, neonates, children, adults), Human Development Index (ie, low-income or high-income countries), and decade and meta-regression using the study period's year as an estimator variable were used.

Main Outcome and Measure

Case fatality ratios of bacterial meningitis.

Results

This review included 371 studies performed in 108 countries from January 1, 1935, to December 31, 2019, describing 157 656 episodes. Of the 33 295 episodes for which the patients' sex was reported, 13 452 (40%) occurred in females. Causative pathogens were reported in 104 598 episodes with Neisseria meningitidis in 26 344 (25%) episodes, Streptococcus pneumoniae in 26 035 (25%) episodes, Haemophilus influenzae in 22 722 (22%), other bacteria in 19 161 (18%) episodes, and unidentified pathogen in 10 336 (10%) episodes. The overall case fatality ratio was 18% (95% CI, 16%-19%), decreasing from 32% (95% CI, 24%-40%) before 1961 to 15% (95% CI, 12%-19%) after 2010. It was highest in meningitis caused by Listeria monocytogenes at 27% (95% CI, 24%-31%) and pneumococci at 24% (95% CI, 22%-26%), compared with meningitis caused by meningococci at 9% (95% CI, 8%-10%) or H influenzae at 11% (95% CI, 10%-13%). Meta-regression showed decreasing case fatality ratios overall and stratified by S pneumoniae, Escherichia coli, or Streptococcus agalactiae (P < .001).

Conclusions and Relevance

In this meta-analysis with meta-regression, declining case fatality ratios of community-acquired bacterial meningitis throughout the last century were observed, but a high burden of disease remained.

Meningitis vaccines in children: what have we achieved and where next?

PURPOSE OF REVIEW

This review highlights the recent impacts of vaccines against the major bacterial causes of meningitis in children, and the challenges for further prevention of bacterial meningitis, with a focus on Streptococcus pneumoniae, Neisseria meningitidis and group B Streptococcus.

RECENT FINDINGS

Conjugate vaccines against S. pneumoniae and N. meningitidis have resulted in dramatic reductions in bacterial meningitis globally where they have been used. Recent licensure and use of capsular group B meningococcal protein vaccines have further reduced meningococcal meningitis in infants, young children and adolescents for countries with endemic disease and during outbreaks.

SUMMARY

Existing vaccines to prevent bacterial meningitis in children should be utilized in countries with significant numbers of cases of pneumococcal and/or meningococcal meningitis. Vaccines, which are able to protect against more than 13 serotypes of S. pneumoniae are in clinical trials and should be able to further reduce pneumococcal meningitis cases. Cost effective meningococcal vaccines against non-A capsular groups are needed for low-resource countries. There remains an urgent need for a vaccine against group B Streptococcus, which is a major cause of neonatal meningitis globally and for which no vaccine currently exists.

Risk scores for outcome in bacterial meningitis: Systematic review and external validation study

OBJECTIVES

To perform an external validation study of risk scores, identified through a systematic review, predicting outcome in community-acquired bacterial meningitis.

METHODS

MEDLINE and EMBASE were searched for articles published between January 1960 and August 2014. Performance was evaluated in 2108 episodes of adult community-acquired bacterial meningitis from two nationwide prospective cohort studies by the area under the receiver operating characteristic curve (AUC), the calibration curve, calibration slope or Hosmer-Lemeshow test, and the distribution of calculated risks.

FINDINGS

Nine risk scores were identified predicting death, neurological deficit or death, or unfavorable outcome at discharge in bacterial meningitis, pneumococcal meningitis and invasive meningococcal disease. Most studies had shortcomings in design, analyses, and reporting. Evaluation showed AUCs of 0.59 (0.57-0.61) and 0.74 (0.71-0.76) in bacterial meningitis, 0.67 (0.64-0.70) in pneumococcal meningitis, and 0.81 (0.73-0.90), 0.82 (0.74-0.91), 0.84 (0.75-0.93), 0.84 (0.76-0.93), 0.85 (0.75-0.95), and 0.90 (0.83-0.98) in meningococcal meningitis. Calibration curves showed adequate agreement between predicted and observed outcomes for four scores, but statistical tests indicated poor calibration of all risk scores.

INTERPRETATION

One score could be recommended for the interpretation and design of bacterial meningitis studies. None of the existing scores performed well enough to recommend routine use in individual patient management.

Meningococcal pneumonia

Neisseria meningitidis remains the most important cause of bacterial meningitis worldwide, particularly in children and young adults. The second most common and a potentially severe end-organ manifestation of invasive meningococcal disease (excluding systemic sepsis) is meningococcal pneumonia. It occurs in between 5% and 15% of all patients with invasive meningococcal disease and is thus the second most common non-systemic end-organ manifestation. To establish the diagnosis requires a high level of clinical awareness - the incidence is therefore very likely underreported and underestimated. This review of 344 meningococcal pneumonia cases reported in the Americas, Europe, Australia, and Asia between 1906 and 2015 presents risk factors, pathogenesis, clinical manifestations, diagnostic approaches, treatment, and prognosis of meningococcal pneumonia.

Nonfunctional variant 3 factor H binding proteins as meningococcal vaccine candidates

Neisseria meningitidis is a human-specific pathogen and leading cause of meningitis and septicemia. Factor H binding protein (fHbp), a virulence factor which protects N. meningitidis from innate immunity by binding the human complement regulator factor H (fH) with high affinity, is also a key antigen in vaccines being developed to prevent meningococcal disease. fHbp can be divided into three variant groups (V1, V2, and V3) that elicit limited immunological cross-reactivity. The interaction of fH with fHbp could impair the immunogenicity of this antigen by hindering access to the antigenic epitopes in fHbp, providing the rationale for the development of nonfunctional fHbps as vaccine candidates. Here, we characterized the two nonfunctional V3 fHbps, fHbp(T286A) and fHbp(E313A), which each contains a single amino acid substitution that leads to a marked reduction in affinity for fH without affecting the folding of the proteins. The immunogenicity of the nonfunctional fHbps was assessed in transgenic mice expressing a single chimeric fH containing domains of human fH involved in binding to fHbp. No differences in anti-V3 fHbp antibody titers were elicited by the wild-type V3 fHbp, V3 fHbp(T286A), and V3 fHbp(E313A), demonstrating that the nonfunctional fHbps retain their immunogenicity. Furthermore, the nonfunctional V3 fHbps elicit serum bactericidal activity that is equivalent to or higher than that observed with the wild-type protein. Our findings provide the basis for the rational design of next-generation vaccines containing nonfunctional V3 fHbps.

Vaccine design reaches the atomic level

The genetic diversity of pathogens presents a challenge to the development of broadly effective vaccines. In this issue, Scarselli et al. combine atomic-level structural information with genomics and classical vaccinology to design a single immunogen that elicits protective immunity against more than 300 natural variants of the bacterial pathogen meningococcus B. This accomplishment provides a glimpse of the power of structure-based vaccine design to create immunogens capable of eliciting protective responses against genetically diverse pathogens.

[Management of chicken pox purpura fulminans: a pediatric case report]

The authors report a case of a 4 years old girl who had presented a chicken-pox purpura fulminans. Lesions appeared 5 days after chicken-pox start and were quickly evoluted in cutaneous and sub-cutaneous necrosis on external side of thighs and behind side of right calf. A medical management was done with fresh plasma, blood, antithrombine 3, and fibrin. Specifics treatments were done: heparin and activated C protein. Surgical treatment was realised 5 weeks later. It consisted of clean necrosis areas and put a thin skin graft witch was took on the scalp. The evolution was fast good. The follow-up is 3 years without big esthetic and functional consequences. Some cases of this pathology were described in literature with serious lesions. The management should be multidisciplinary. Surgical treatment should be realised when lesions are stabilized. Scalp is a donor site for skin graft very interesting because of big quantity of skin and not esthetic consequence.

Mutations in folP associated with elevated sulfonamide MICs for Neisseria meningitidis clinical isolates from five continents

Sulfonamide resistance in meningococci is associated with mutations in the chromosomal gene folP, which encodes dihydropteroate synthase. Several mutations associated with resistance have been previously described, including amino acid substitutions at codons 31 and 194, a glycine-serine insertion at codons 195 and 196, and, recently, an additional mutation at nucleotide 682 (C682A). In this study, sulfisoxazole MICs were determined for 424 geographically diverse clinical isolates of Neisseria meningitidis, including all major subtypes. A subset of 134 isolates with MICs ranging from 0.5 to >64 microg/ml were assayed for the C682A mutation by real-time PCR, and 25 isolates were selected for folP gene sequencing. All isolates for which the sulfisoxazole MIC was >/=8 possessed the C682A mutation by real-time PCR or folP sequencing, and 34 of 35 isolates with a MIC of </=2 lacked this mutation. Of 16 sequenced isolates for which the sulfisoxazole MIC was >/=4, 15 possessed previously described mutations, including 10 at codon 31, 1 at codon 194, and 4 with the 2-amino-acid insertion codons 195 and 196; all 16 possessed the C682A mutation. The C682A mutation predicted elevated sulfonamides MICs for a large number of geographically diverse clinical isolates of meningococci. Detection of this mutation by real-time PCR or other methods may allow more wide-scale detection of meningococcal isolates with for which the sulfonamide MICs are elevated without resorting to multiple assays or folP gene sequencing, providing a simple, high-throughput screening method for use in public health and epidemiologic settings.

Plastic surgery management in pediatric meningococcal-induced purpura fulminans

Purpura fulminans associated with meningococcemia is a devastating disease in children. The tissue loss can be extensive and difficult to determine at the outset. The authors suggest a strategy to manage these wounds with the goal of preserving as much tissue and function as possible. At the present time, conservative therapy to the wounds appears to be the best course in the initial, critical phase, as long as no active local purulence is found. Debridement or amputation is performed when the nonviable tissue margins are delineated. Temporary coverage with allograft may be required; definitive coverage is accomplished when the local tissue perfusion has recovered. Future revisions are often necessary to improve these children's quality of life.

Genomic polymorphic profiles in an Irish population with meningococcaemia: is it possible to predict severity and outcome of disease?

Patients with meningococcal disease have increased plasma levels of proinflammatory cytokines IL-6, IL-1beta, and TNF-alpha, with higher levels associated with fatal outcome. This study investigated whether polymorphisms in genes encoding these cytokines, and in those encoding anti-inflammatory IL-10 and IL-1Ra, are associated with the outcome in patients with meningococcal disease. Seven polymorphisms were genotyped in 183 meningococcal disease patients and 389 controls. The IL-6 -174 G/G and IL-10 -1082 A/A genotypes were more frequent in nonsurvivors compared with survivors (P=0.023 IL-6, 0.25 IL-10), and in patients with severe disease compared to those with mild disease (P=0.037 IL-6, 0.0078 IL-10). An association was also found between meningococcal disease and the IL-1RN VNTR polymorphism, but no association was observed with the LTA +252, TNF -308, IL-10 -592, or IL-1B +3953 polymorphisms. We conclude that genetic variability in the IL-6, IL-10, and IL-1RN genes is associated with a poor outcome in meningococcal disease.

PCR and restriction endonuclease assay for detection of a novel mutation associated with sulfonamide resistance in Neisseria meningitidis

We identified a previously undocumented mutation in the dihydropteroate synthase (folP) gene associated with Neisseria meningitidis sulfonamide resistance. A PCR-based assay to detect this mutation, which is 100% predictive of sulfonamide resistance, was developed.

Vaccination against Neisseria meningitidis using three variants of the lipoprotein GNA1870

Sepsis and meningitis caused by serogroup B meningococcus are devastating diseases of infants and young adults, which cannot yet be prevented by vaccination. By genome mining, we discovered GNA1870, a new surface-exposed lipoprotein of Neisseria meningitidis that induces high levels of bactericidal antibodies. The antigen is expressed by all strains of N. meningitidis tested. Sequencing of the gene in 71 strains representative of the genetic and geographic diversity of the N. meningitidis population, showed that the protein can be divided into three variants. Conservation within each variant ranges between 91.6 to 100%, while between the variants the conservation can be as low as 62.8%. The level of expression varies between strains, which can be classified as high, intermediate, and low expressors. Antibodies against a recombinant form of the protein elicit complement-mediated killing of the strains that carry the same variant and induce passive protection in the infant rat model. Bactericidal titers are highest against those strains expressing high yields of the protein; however, even the very low expressors are efficiently killed. The novel antigen is a top candidate for the development of a new vaccine against meningococcus.

Development of vaccines against meningococcal disease

Neisseria meningitidis is a major cause of bacterial meningitis and sepsis. Polysaccharide-protein conjugate vaccines for prevention of group C disease have been licensed in Europe. Such vaccines for prevention of disease caused by groups A (which is associated with the greatest disease burden worldwide), Y, and W135 are being developed. However, conventional approaches to develop a vaccine for group B strains, which are responsible for most cases in Europe and the USA, have been largely unsuccessful. Capsular polysaccharide-based vaccines can elicit autoantibodies to host polysialic acid, whereas the ability of most non-capsular antigens to elicit broad-based immunity is limited by their antigenic diversity. Many new membrane proteins have been discovered during analyses of genomic sequencing data. These antigens are highly conserved and, in mice, elicit serum bactericidal antibodies, which are the serological hallmark of protective immunity in man. Therefore, there are many promising new vaccine candidates, and improved prospects for development of a broadly protective vaccine for group B disease, and for control of all meningococcal disease.

The use of simultaneous free latissimus dorsi tissue transfers for reconstruction of bilateral upper extremities in a case of purpura fulminans

We report a case of extensive purpura fulminans destroying the soft tissue over the posterior aspect of both elbows. Simultaneous, bilateral free latissimus dorsi muscle transfers were used to close both wounds in a single procedure. The wounds resulting from severe purpura fulminans can be extensive and limb threatening. The simultaneous transfer of 2 free flaps can provide expeditious soft tissue repair while minimizing the risk of repeat anesthesia in these critically ill patients. We found that certain details concerning planning and performing the procedure fostered its successful outcome.

Update on meningococcal disease with emphasis on pathogenesis and clinical management

The only natural reservoir of Neisseria meningitidis is the human nasopharyngeal mucosa. Depending on age, climate, country, socioeconomic status, and other factors, approximately 10% of the human population harbors meningococci in the nose. However, invasive disease is relatively rare, as it occurs only when the following conditions are fulfilled: (i) contact with a virulent strain, (ii) colonization by that strain, (iii) penetration of the bacterium through the mucosa, and (iv) survival and eventually outgrowth of the meningococcus in the bloodstream. When the meningococcus has reached the bloodstream and specific antibodies are absent, as is the case for young children or after introduction of a new strain in a population, the ultimate outgrowth depends on the efficacy of the innate immune response. Massive outgrowth leads within 12 h to fulminant meningococcal sepsis (FMS), characterized by high intravascular concentrations of endotoxin that set free high concentrations of proinflammatory mediators. These mediators belonging to the complement system, the contact system, the fibrinolytic system, and the cytokine system induce shock and diffuse intravascular coagulation. FMS can be fatal within 24 h, often before signs of meningitis have developed. In spite of the increasing possibilities for treatment in intensive care units, the mortality rate of FMS is still 30%. When the outgrowth of meningococci in the bloodstream is impeded, seeding of bacteria in the subarachnoidal compartment may lead to overt meningitis within 24 to 36 h. With appropriate antibiotics and good clinical surveillance, the mortality rate of this form of invasive disease is 1 to 2%. The overall mortality rate of meningococcal disease can only be reduced when patients without meningitis, i.e., those who may develop FMS, are recognized early. This means that the fundamental nature of the disease as a meningococcus septicemia deserves more attention.

Update on meningococcal disease with emphasis on pathogenesis and clinical management

The only natural reservoir of Neisseria meningitidis is the human nasopharyngeal mucosa. Depending on age, climate, country, socioeconomic status, and other factors, approximately 10% of the human population harbors meningococci in the nose. However, invasive disease is relatively rare, as it occurs only when the following conditions are fulfilled: (i) contact with a virulent strain, (ii) colonization by that strain, (iii) penetration of the bacterium through the mucosa, and (iv) survival and eventually outgrowth of the meningococcus in the bloodstream. When the meningococcus has reached the bloodstream and specific antibodies are absent, as is the case for young children or after introduction of a new strain in a population, the ultimate outgrowth depends on the efficacy of the innate immune response. Massive outgrowth leads within 12 h to fulminant meningococcal sepsis (FMS), characterized by high intravascular concentrations of endotoxin that set free high concentrations of proinflammatory mediators. These mediators belonging to the complement system, the contact system, the fibrinolytic system, and the cytokine system induce shock and diffuse intravascular coagulation. FMS can be fatal within 24 h, often before signs of meningitis have developed. In spite of the increasing possibilities for treatment in intensive care units, the mortality rate of FMS is still 30%. When the outgrowth of meningococci in the bloodstream is impeded, seeding of bacteria in the subarachnoidal compartment may lead to overt meningitis within 24 to 36 h. With appropriate antibiotics and good clinical surveillance, the mortality rate of this form of invasive disease is 1 to 2%. The overall mortality rate of meningococcal disease can only be reduced when patients without meningitis, i.e., those who may develop FMS, are recognized early. This means that the fundamental nature of the disease as a meningococcus septicemia deserves more attention.

Which contacts of patients with meningococcal disease carry the pathogenic strain of Neisseria meningitidis? A population based study

OBJECTIVES

To determine the prevalence of the pathogenic strain of Neisseria meningitidis in contacts of patients with meningococcal disease, and to determine which contact groups are likely to be carriers and warrant chemoprophylaxis.

DESIGN

Population based study.

SETTING

Norwegian county of Telemark.

SUBJECTS

1535 primary contacts of 48 patients with meningococcal disease, and 78 secondary contacts.

INTERVENTIONS

Carriers of the pathogenic strain were treated with rifampicin. All household members and kissing contacts under 15 years of age were treated with oral penicillin. Contacts were taught to recognise the symptoms of meningococcal disease.

RESULTS

In 27 of 48 cases investigated, contacts carrying the pathogenic strain of N meningitidis were found. A total of 42 such contacts were identified. Contacts were stratified into three classes according to the assumed closeness of contact with patients. In class 1 (household members and kissing contacts) the prevalence of the pathogenic strain was 12.4% (95% confidence interval 5.5% to 19.3%). In classes 2 and 3 the prevalence was 1.9% (0.9% to 3.4%) and 1.6% (0.14% to 3.1%).

CONCLUSIONS

There is a high rate of carriage of the pathogenic strain of N meningitidis in patients' household members and kissing contacts, and this supports the practice of giving chemoprophylaxis to these contacts. The prevalence of carriage among other contacts is 2-3 times that found in the general population (0.7%); the benefits of chemoprophylaxis to these contacts may be marginal.

A normal platelet count at admission in acute meningococcal disease does not exclude a fulminant course

OBJECTIVE

To determine the value of the platelet count at admission for the assessment of the severity of disease in acute meningococcal infections.

DESIGN

Retrospective and prospective, descriptive patient study.

SETTING

University Hospital Intensive Care Unit (ICU).

PATIENTS

All patients (n = 92) with acute meningococcal disease from 1985 to 1997, who arrived at the ICU within 12 h after hospital admission and had more than one platelet count during the first 12 h.

MEASUREMENTS AND RESULTS

After admission, platelets dropped in 95% of the patients. At admission, 2/41 (5%) of the non-hypotensive patients and 13/51 (25%) of the hypotensive patients had platelets fewer than 100 x 10(9)/l. During the following 12 h, these percentages increased to 15% and 71%, respectively. Fatalities had, at admission, a median platelet count of 111 x 10(9)/l (range, 19-302 x 10(9)/l), whereas the nadir, occurring at median 7.0 h (range, 1.3-12 h), was 31 x 10(9)/l (range, 12-67 x 10(9)/l). Plasma TNF, measured shortly after admission, correlated better with the platelet nadir (r = -0.65, p < 0.0001) than with the platelet count at admission. Similarly, serum lactate correlated better with the platelet nadir.

CONCLUSIONS

As platelets drop after admission, the use of the platelet count at admission for the assessment of the prognosis in acute meningococcal disease may be misleading. Frequently repeated platelet counts are a better tool for evaluating the severity of disease.

Meningococcal meningitis among Rwandan refugees: diagnosis, management, and outcome in a field hospital

OBJECTIVE

To study the diagnostic process, clinical course, and outcome of Rwandan refugees with meningococcal meningitis, treated in an Israeli field hospital in Goma, Zaire, in the summer of 1994.

METHODS

Patient hospital charts and laboratory records were reviewed with critical evaluation of clinical presentation and diagnostic tests. Patients were treated as part of a disaster relief effort in a refugee camp experiencing several coexisting lethal epidemics.

RESULTS

A total of 65 patients were identified as having group A meningococcal meningitis. Latex agglutination test for Neisseria meningitidis soluble antigen in the cerebrospinal fluid was found to be a superior diagnostic tool, as compared to Gram stain, and at least as effective as culture. The mortality rate was 14%; mortality was markedly affected by co-morbidity (e.g., dysentery, pneumonia, and malnutrition).

CONCLUSIONS

The outcome of patients with meningococcal meningitis, treated in referral centers within a disaster area may be favorable, despite overwhelming coexisting epidemics, and may be comparable to that achieved in advanced medical facilities. Encephalopathy may be a diagnostic pitfall in the perspective of coexisting epidemics, requiring a high index of suspicion and routine lumbar puncture. The latex agglutination test is highly useful in achieving prompt diagnosis of meningococcal meningitis, in particular when sample handling for culture and microscopy is suboptimal.

Meningococcemia

Meningococcal infection is a contagious disease that is spread via the respiratory route through pharyngeal secretions. Clinical manifestations range from occult bacteremia to overwhelming septicemia or meningitis. Skin manifestations often develop and may be the first sign that leads to clinical suspicion of meningococcemia. Treatment consists of antibiotic therapy and supportive care, which may include aggressive fluid resuscitation, oxygen, ventilatory support, and inotropic support. The use of chemoprophylaxis and in certain circumstances vaccination are important in preventing secondary cases of meningococcal disease.

Meningococcal disease in Norway 1992-1995. Epidemiology and fatality

We analysed data on all cases of meningococcal disease (MCD) reported to the Norwegian Notification System for Infectious Diseases during the period 1992-1995. For 1994, additional information on fatalities was gathered. Notifications were received from laboratories and clinicians. A total of 586 patients were included. The incidence decreased from 4.6 per 100000 in 1992 to 2.4 in 1994, and then rose to 3.7 in 1995. The initial decrease, a trend also observed in previous years, was seen in both main serogroups B and C. This decline was broken with the increase of serogroup B in 1995. MCD predominantly affects children below 5 years and teenagers. In 1994, 17/105 (16%) patients died. Main risk factors for fatal outcome were age above 30 years (adjusted odds ratio (OR) 19.8; 95% confidence interval (CI) 2.4-164), septicaemia (adjusted OR 9.5; 95% CI 2.2-41) and disease caused by strains B:15 (adjusted OR 6.4; 95% CI 1.2-35) or C:2a (adjusted OR 10.1; 95% CI 1.6-62). We conclude that the incidence of MCD in Norway is unpredictable and that the case fatality rate is substantially higher than previously believed.

The changing presentations of meningococcal disease

Meningococcal disease (MCD) can present as meningitis, meningitis plus septicaemia or septicaemia alone. This 17-year retrospective study sought to determine if the proportion of cases presenting as septicaemia alone was increasing. Four hundred and forty-nine children with MCD were admitted between 1977 and 1993, 50 children died (11%). The proportion of cases with septicaemia alone increased from 7% in 1977-1985 to 36% in 1990-1993 (P < 0.0005). Mortality was highest in children with septicaemia alone (19%). Despite the increase in septicaemia, overall mortality did not alter over the 17 years.

CONCLUSION

MCD should not be thought of as "meningitis", since 33% of cases now present as septicaemia alone. Nearly one in five children with septicaemia alone die. Information and publicity about MCD should focus on septicaemia, characterised by a petechial rash, as the life-threatening presentation.

Patient and strain characteristics in relation to the outcome of meningococcal disease: a multivariate analysis

To investigate the joint association of patient and strain characteristics with the outcome of meningococcal disease (MD), data were collected on 563 consecutive cases of MD reported between 1989 and 1990 in The Netherlands. The meningococcal isolates were characterized with regard to their surface characteristics. Sequelae occurred in 8.5% of the patients, and were only associated with the presence of bacteraemia. The case-fatality rate was 7.7%. Infants aged < or = 5 months and patients in the age-groups of 10-19 years and > or = 50 years had an increased risk for a fatal outcome compared with children from 6 months to 9 years old (Odds Ratios [ORs]: 5.1, 3.4 and 9.8, respectively). The OR for females versus males was 2.3. The ORs for patients with bacteraemia, or a combination of bacteraemia and meningitis, compared with meningitic patients, were 2.3 and 3.1. Meningococcal strain characteristics did not influence the case-fatality rate substantially. In conclusion, host factors were found to be determinants for a fatal outcome of MD in The Netherlands from 1989 to 1990.

Prognostic factors in meningococcal disease and a new scoring system

One-hundred-and-forty patients diagnosed as having meningococcal disease have been investigated retrospectively with respect to prognostic factors. The overall mortality was 8.6%, the mortality rate of the infants under 6 months of age being higher than that of the other groups. In cases where there was no meningitis or leucocytosis, the presence of hypotension, disturbed consciousness and diffuse petechiae increased the mortality rate significantly. High fever did not have any effect on mortality. We propose a new practical and reliable scoring system for meningococcal disease for determining the influence of prognostic factors on mortality.

Endotoxin liberation from Neisseria meningitidis correlates to their ability to induce procoagulant and fibrinolytic factors in human monocytes

Endotoxin released from different strains of Neisseria meningitidis were studied for their ability to induce procoagulant (tissue factor, TF), fibrinolytic (plasminogen activator, PA) and antifibrinolytic (plasminogen activator inhibitor 2, PAI-2) factors in human monocytes. Two meningococcal strains that liberate endotoxin (E+; 270+ and 840+) and 2 non-liberating (E-; 270- and 840-) strains were used. The endotoxin activity in culture filtrates of these strains was monitored with the Limulus amoebocyte lysate (LAL) test. There was a marked difference between E+ and E- strains in their ability to liberate endotoxin. Suspensions of whole bacteria of all 4 strains induced a significant (14-19-fold) increase in monocyte TF expression when present in concentrations > 10(5) CFU/ml. At lower concentrations (10(4) CFU/ml), E+ strains were clearly more potent stimulators of TF synthesis than E- strains. Culture filtrates of E+ strains were up to 10(4)-fold more potent in inducing TF synthesis than filtrates from E- strains. This marked difference in inducing potency between E+ and E- strains was also observed when monocyte PAI-2 synthesis was examined. The PA expression, on the other hand, was suppressed when monocytes were incubated in the presence of culture filtrates, especially filtrates from the E+ strains. The increased procoagulant and antifibrinolytic activity, together with reduced profibrinolytic activity of monocytes, was closely correlated to the amount of endotoxin measured in the culture filtrates. These changes may contribute substantially to the coagulopathic state seen during systemic meningococcal disease.

Transformational exchanges in the dihydropteroate synthase gene of Neisseria meningitidis: a novel mechanism for acquisition of sulfonamide resistance

The nucleotide sequences of the chromosomal dihydropteroate synthase (dhps) genes in sulfonamide-susceptible and sulfonamide-resistant strains of Neisseria meningitidis of serogroups A, B and C were determined. The molecular weights and the amino acid sequences showed similarity to those of all other known dihydropteroate synthase polypeptides. Sequence comparison of the N. meningitidis dhps genes indicated horizontal transfer of DNA segments rather than point mutations as the cause for resistance in meningococci. The dhps genes in three of four sulfonamide-resistant meningococci contained identical central regions of 424 bp. Compared with the corresponding genes in susceptible strains, each central region included an insert of 6 bp. In one of the sulfonamide-resistant strains, the dhps gene was similar to the corresponding genes in the sensitive strains in its NH2-terminal and C-terminal parts. Its central region, however, was identical to the corresponding regions of two of the other resistant genes, and thus it could be seen as a hybrid dhps gene. Transformation experiments and mapping of transformed dhps genes indicated the existence of a novel mechanism for the dissemination of sulfonamide resistance in N. meningitidis. The origin of the resistance-mediating segment of the gene is unknown, but hybridization results showed the presence of homologous dhps genes in Neisseria gonorrhoeae and N. lactamica but not in N. subflava or Branhamella catarrhalis.

Structural characterization of the lipid A component of pathogenic Neisseria meningitidis

The lipid A component of meningococcal lipopolysaccharide was structurally characterized by using chemical modification methods, methylation analysis, 31P nuclear magnetic resonance, and laser desorption mass spectroscopy. It was shown that Neisseria meningitidis lipid A consists of a 1,4'-bisphosphorylated beta(1'----6)-linked D-glucosamine disaccharide (lipid A backbone), both phosphate groups being largely replaced by O-phosphorylethanolamine. This disaccharide harbors two nonsubstituted hydroxyl groups at positions 4 and 6', the latter representing the attachment site of the oligosaccharide portion in lipopolysaccharide. In addition, it is substituted by up to six fatty acid residues. In the major lipid A component, representing a hexaacyl species, the hydroxyl groups at positions 3 and 3' carry (R)-3-hydroxydodecanoic acid [12:0(3-OH)], whereas the amino groups at positions 2 and 2' are substituted by (R)-3-(dodecanoyloxy)tetradecanoic acid [3-O(12:0)-14:0]. A minor portion was present as a tetraacyl lipid A component lacking either dodecanoic acid (12:0) or 12:0 and 12:0(3-OH). N. meningitidis lipid A, therefore, significantly differs from Escherichia coli lipid A by the nature and locations of fatty acids and the substitution of O-phosphorylethanolamine for the nonglycosyl (4'-P) and glycosyl phosphate.

Cloning and characterization of a DNA fragment that confers sulfonamide resistance in a serogroup B, serotype 15 strain of Neisseria meningitidis

By cloning studies and complementation experiments, the sulfonamide resistance gene of a serogroup B and serotype 15 (B:15) strain of Neisseria meningitidis was localized to a 1.2-kb chromosomal SspI fragment expressing a drug-resistant dihydropteroate synthase. The fragment hybridized to DNA from both resistant and susceptible strains, suggesting that the resistance gene is a variant of the normal gene for dihydropteroate synthase.

Endotoxin release from neisseria meningitidis. Relationship between key bacterial characteristics and meningococcal disease

A method was established in order to measure total and filtrable (CF) endotoxin in cultures of Neisseria meningitidis strains. The Limulus lysate (LAL) test gave results which paralleled those of the standard rabbit pyrogen test and of gas chromatography (GLC), concerning detection of different CF endotoxin levels. Meningococci varied in their ability to produce CF endotoxin. Cultures of similar bacterial densities, whether with a high (E+) or a low (E-) release of endotoxin in CF, had both high yields of endotoxin in sonicated culture suspensions determined by the LAL test. GLC demonstrated only small differences in total LPS contents between E+ and E- strains. This suggests that strains with similar cell wall endotoxin contents may vary in CF endotoxin. Electron microscopy revealed that E+ strains presented a high number of free, outer cell wall fragments (blebs, tubuli, membranes and aggregates of such structures) in surroundings. Few such free, small structures were found around E- strains. The amount of CF endotoxin of E+ strains was in part a function of the number of colony forming units (CFU/ml), and generally followed the growth curve. Because of its moment of appearance, and also based on electron microscopy findings, CF endotoxin appeared mainly to be released from living bacteria. The CF level of endotoxin was low or not detected at all in cultures of E- strains although their cultures reached higher mean CFU-levels than the niveaus required for the detection of CF endotoxin in the E+ strains. The E+ property was strain dependent. Meningococci isolated from CSF or blood had a significantly higher proportion of E+ strains (88.2%) and a higher CF endotoxin titre (greater than or equal to 10(3); 34.5%), than isolates from carriers (32.3% and 10.8%, respectively) (p less than 0.001 and p less than 0.001, respectively). A high mean CFU/ml in cultures seemed to be more often associated with isolates from patients than from carriers, more often with the presence than abscence of capsular polysaccharide (p less than 0.05), and more often with the presence than absence of the E+ property (p = 0.002). E+ strains were mostly serogroupable (i.e. encapsulated), regardless of source of the isolate (99% case and 80% carrier isolates). In contrast, serogroupable bacteria were not necessarily E+ when isolated from carriers (54.8%). The serogroup most apt to cause disease tended to have the highest proportion of E+ strains and the highest level of CF endotoxin.(ABSTRACT TRUNCATED AT 400 WORDS)

Development and characterization of an anti-idiotype antibody to the capsular polysaccharide of Neisseria meningitidis serogroup C

A monoclonal anti-idiotypic antibody (Ab2) whose antibody combining site contained a surrogate image of the meningococcal group C capsular polysaccharide was developed. To accomplish this, a monoclonal antibody against the group C capsular polysaccharide was developed by the fusion of splenocytes from mice immunized with Neisseria meningitidis group C strain MP13 with Sp2/0-Ag14 plasmacytoma cells. Monoclonal antibody 1E4, an immunoglobulin M isotype, demonstrated binding to the serogroup C polysaccharide in enzyme-linked immunosorbent assay (ELISA). Monoclonal antibody 1E4 reacted with 30 of 30 group C strains and 1 of 36 group B strains in immunodot assay, slide agglutination, inhibition ELISA, and bactericidal assay. This monoclonal antibody was selected as idiotype (Ab1) for the development of hybridomas producing an anti-idiotype antibody. One of the hybridomas developed, designated 6F9, was capable of over 70% inhibition of 1E4 in binding in the meningococcal C polysaccharide-specific ELISA. Studies with convalescent human serum demonstrated 100% inhibition of a serogroup C-specific ELISA with 200 micrograms of 6F9 per ml and 50% inhibition of this ELISA was achieved with 50 micrograms of 6F9 per ml. Monoclonal anti-idiotype antibodies (Ab3) with specificities similar to Ab1, 1E4 were generated from BALB/c mice immunized with the Ab2 (6F9). Immunization of rabbits with 6F9 resulted in an immunoglobulin G response which was significantly greater than that of control to a titer of 1:160. These studies indicate that monoclonal 6F9 contained a surrogate image on the combining antibody site which mimicked meningococcal C polysaccharide. This surrogate image is capable of evoking antibodies to the meningococcal C polysaccharide in syngenic and xenogenic species.

Antimicrobial therapy and case fatality in meningococcal disease

The effect of different initial antimicrobial treatments on the case fatality rate (CFR) was evaluated in 112 consecutive patients with meningococcal disease. The overall CFR was 9.8%. 85 patients received initial therapy with chloramphenicol in addition to benzylpenicillin or other antimicrobials, and 27 patients benzylpenicillin or other antimicrobials without chloramphenicol. Patients treated with chloramphenicol had a lower CFR than those not given chloramphenicol (5% vs. 26%; p = 0.004). However, severely ill patients were treated more often with penicillins, and adjustment for the severity of disease on admission to hospital demonstrated that this difference in favour of chloramphenicol was slight and nonsignificant (p = 0.58). High doses of benzylpenicillin and no chloramphenicol were also associated with a higher CFR than low doses. However, the difference was not significant (p = 0.22). More extensive studies should be carried out to evaluate the effect of benzylpenicillin doses and chloramphenicol on the outcome of meningococcal disease.

Endotoxin liberation from Neisseria meningitidis isolated from carriers and clinical cases

Endotoxin liberation was studied in a blinded material of 121 Neisseria meningitidis isolates; from nasopharynx of 58 carriers and from cerebrospinal fluid or blood of 63 cases with meningococcal disease. Endotoxin activity in culture filtrates was determined by a Limulus lysate test. Meningococci isolated from clinical cases were significantly more frequently endotoxin-liberating (E+) (84.1%) than in carriers (25.9%); p less than 0.001. Serogroupable carrier isolates had a significantly higher frequency of E+ meningococci (61.9%) than non-groupable ones (5.4%); p less than 0.002. Serogroup B case isolates, which generally had a larger amount of capsular polysaccharide than B meningococci from carriers, had a significantly higher proportion of E+ meningococci than group B from carriers; p = 0.007. All 7 serogroup C isolates were E+ (5 cases and 2 carriers). No correlation was found between endotoxin liberation and the serotype: subtype 15:P1.16, tested by a selection of monoclonal antibodies, or between endotoxin liberation and sulfonamide resistance, when carrier and case isolates were studied separately. Meningococci isolated from cases had the following mean endotoxin titres: 320.5 in the meningitis group, 408.2 in the septicaemic group, 462.1 in the septicaemic and meningitis group, and 123.7 in the group with other systemic disease. E+ meningococci were isolated from 5/6 fatal cases. Thus, endotoxin liberation from meningococci is strongly, but not completely associated with establishment of meningococcal disease and with the presence of capsular polysaccharide.

Endotoxin release from invasive meningococci related to sulfonamide resistance, serogroup and serotype

The relationship between endotoxin liberation, sulfonamide resistance, serogroups and serotypes was studied in 28 Neisseria meningitidis strains isolated from patients with meningococcal disease. Sulfonamide resistance was present in 15/28 strains. 22 strains belonged to serogroup B, and 5 to group C; 1 strain was non-groupable. Free endotoxin activity in growing cultures of meningococci with endotoxin titre of greater than or equal to 10(2) was found in 27/28 strains. A high endotoxin activity was present in both sulfonamide-sensitive and -resistant invasive meningococci. A high endotoxin release with titre greater than or equal to 10(3) seemed to be more associated with serogroup C than B, and more to the serotypes 2 and 15/16 than to the non-typable strains.

Case fatality of meningococcal disease in western Norway

In the period 1976-84, 211 patients hospitalized with meningococcal disease were examined for possible relation between various epidemiological parameters and fatality. The peak incidences were in the age groups 0-4 and 13-18 years, with teenage girls peaking 2 years ahead of the boys. The overall case fatality rate was 8.5%. In septicemic patients (without meningitis) hypotension and/or ecchymoses on admission correlated strongly with a poor prognosis. Most deaths occurred during the months of March and November, and none during the summer months. There was a significant clustering of deaths among patients admitted during the morning hours, probably due to delayed diagnosis and treatment during the night. Since almost all patients who died had skin bleedings on admission, frequent examination of the skin in cases with acute unexplained fever might have saved lives.

Surgical management of life-threatening and disfiguring sequelae of fulminant meningococcemia

In recent years, because of prompt diagnosis and effective, aggressive resuscitation, the majority of infants and children with fulminant meningococcemia are surviving. From 1974 through 1984, 135 patients with this diagnosis were treated, and 126 of them survived. Although a purpuric skin rash developed in almost all of these patients initially, in eight of them it progressed to multiple confluent areas of cutaneous gangrene, usually associated with extensive necrosis of underlying subcutaneous fat, fascia, skeletal muscle, and even bone. Tissue necrosis seemed to be most extensive in regions of reduced blood flow, such as the extremities, but it almost never followed a pattern of anatomic vascular distribution. A most significant microscopic finding was the presence of multiple fibrin thrombi in vessels, often in close proximity with the foci of tissue necrosis. Five children who ranged in age from 6 months to 12 years required operation. Initially, all surface wounds were treated like full-thickness burns with silver sulfadiazene (Silvadene) dressings. Once the patient's condition had stabilized and the extent of tissue necrosis was apparent, all necrotic tissue was excised and the resulting wounds were temporarily covered with biologic dressings to assure a clean, viable base for skin grafting. Because the resulting quality of life postoperatively in all five surviving patients has been satisfactory, we recommend an aggressive surgical approach in patients with fulminating meningococcemia, despite what may initially appear to be devastating and even lethal complications of this disease.

An outbreak of group B meningococcal disease: tracing the causative strain of Neisseria meningitidis by DNA fingerprinting

Following an outbreak of meningococcal disease in three schoolchildren in a small community in northern Norway, DNA fingerprinting, serotyping with monoclonal antibodies, serogrouping, and sulfonamide sensitivity testing were applied for characterization and tracing of the causative agent. The three case isolates were genomically indistinguishable, sulfonamide-resistant, serogroup B, serotype 15 meningococci. Throat specimens were collected from 552 healthy contacts, including all children below age 17 and their parents. Among the 36 carrier isolates (carrier rate, 6.5%) 13 showed DNA fingerprints identical, or almost identical, to the index pattern. All of these 13 isolates were sulfonamide resistant, 12 were of serotype 15, and 8 were of polysaccharide serogroup B (5 were nongroupable). These closely related isolates were almost exclusively recovered from schoolchildren of 2 of 15 small villages, one of which included the homes of two of the patients. The remaining 23 carrier isolates were nonresistant, non-type 15 meningococci of widely differing DNA restriction patterns. Our results confirm that DNA fingerprinting has potential as an efficient tool in practical meningococcal epidemiology.

Meningococcal infections in Scotland 1972-82

Strains of Neisseria meningitidis isolated from patients with meningitis or septicaemia without meningitis in Scotland during the years 1972-82 have been reviewed together with details of the age, sex, disease and outcome of the patients from whom they were isolated. A total of 1185 strains were isolated, of which 927 were examined at the Meningococcal Reference Laboratory (Scotland): 19.3% were of serogroup A, 63% of group B, 9.6% of group C, 6% of W135 and 1.6% of other groups. Non-groupable strains were rare. Disease was most common in the first years of life but there was a difference in the age distribution of disease due to the different serogroups, the proportion of disease due to group B being smaller in adults than that due to other serogroups. The overall mortality in meningitis was 7.5% and in septicaemia was 20.6%, although there were differences between the rates for the various serogroups. The serogroup distribution differed in disease as opposed to meningococci isolated from carriers although group B strains were predominant in both series. Overall, approximately 15% of strains were resistant to sulphadiazine, the proportion of resistant group A strains being higher than that of other serogroups.

Mortality in meningococcal disease in Belgium

A survey of children admitted with meningococcal disease to 53 paediatric units in Belgium between 1975 and 1979 was made in order to assess the case mortality rate (CMR) and to identify risk factors associated with death. A total of 309 cases (226 bacteriologically confirmed and 83 unconfirmed) was recorded. The overall CMR was 6.1 per cent. It was 4.4 for bacteriologically confirmed cases and 10.8 for unconfirmed cases. The CMR was higher for septicaemia without meningitis (22.2 per cent) than for meningitis with or without signs of septicaemia (3.4 per cent). The risk of death was not related to the sex or nationality of the patients. Age was a major determinant of the CMR, independently of the clinical picture. The highest risk of death was in children under one year of age. Poor socio-economic conditions were a significant risk factor. Failure to recognise the severity of the disease by some poorly educated mothers, and the admission of the patient to a hospital lacking adequate facilities for managing severely affected children, were the two significant causes of delay of adequate treatment.

Effect of benzylpenicillin in mice infected with endotoxin-liberating or non-liberating variant strains of Neisseria meningitidis

The effect of benzylpenicillin treatment was studied in mice infected intraperitoneally (i.p.) with endotoxin-liberating (E+) and non-liberating (E-) meningococci derived from the same original serogroup B strain. The E+ meningococci were significantly more virulent to mice than the E- variants in untreated animals (p less than 0.001). Large doses of benzylpenicillin given intravenously (i.v.) immediately after i.p. inoculation of E+ or E- meningococci resulted in complete, or almost complete survival. When treatment started later the number of surviving E- infected animals increased in all treatment regimens. By contrast, E+ infected animals had one or more treatment groups in all regimens that did not respond to benzylpenicillin at all. Benzylpenicillin treatment was given over a period of time as intermittent, regular i.v. doses, or as a depot preparation subcutaneously (s.c.). The mortality observed in E+ infected mice after benzylpenicillin i.v. was 75%, after benzylpenicillin procaine s.c. 82.5%, while animals receiving only saline i.v. had a mortality of 67.5%. The corresponding mortalities for E- infected animals were 15% (p = 0.0014), 42.5%, and 42.5%, respectively.

Sulfonamide resistance in Neisseria meningitidis strains liberating various amounts of free endotoxin

The relationship between sulfonamide susceptibility and the ability to liberate endotoxin was studied in 50 strains of Neisseria meningitidis. The endotoxin activity was investigated by the Limulus lysate test in growing cultures of 25 sulfonamide-resistant and 25 sensitive strains. The sulfonamide-resistant strains tended to have a higher endotoxin activity in cultures grown for 6 h than sensitive ones, and had also a higher amount of free, filtrable endotoxin.

Meningococcal disease in Scandinavia

Scandinavia (Denmark, Finland, Iceland, Norway, and Sweden) comprises with mutual borders and 22.3 million inhabitants an area where the socioeconomic and cultural conditions are similar. Epidemic diseases, such as meningococcal infection, might therefore be expected to be uniformly distributed. An epidemiological study in the 10-year period 1970-9 shows, however, remarkable differences in the incidence, age, and serogroup and type distribution, as well as in the general dynamics of the disease. Three epidemics, two caused by different serotypes of group B (Norway and Iceland) and one by group A (Finland) occurred within the observation period. The annual overall incidence was generally around 3/100 000 but increased from fivefold (Finland) to eightfold (northern Norway) during epidemics. The epidemic strains caused infection in over 3000 patients and the loss of at least 250 lives. The overall case fatality rate was 8.6% (range 4.1-13.7%). Men were more susceptible and had a worse prognosis than women of the same age group. The group A epidemic in Finland was influenced by a large vaccination campaign, but this possibility was not feasible in the two other epidemics.

Effect of penicillin on the morphology of a Neisseria meningitidis strain liberating free endotoxin. An electron microscope study

An endotoxin-liberating strain of Neisseria meningitidis plasmolysed extensively after 2 h of exposure to 100 times MIC values of benzypenicillin. The peptidoglycan layer could be demonstrated after 2 h of treatment in places where the cytoplasm still was close to the cell wall. After 20 h, however, this layer was complete undetectable. In untreated cells the peptidoglycan layer could more easily be found in older cultures than in very young cultures. An increased adhesiveness and aggregation to other bacterial cells and to cell wall material could be observed after 2 h of penicillin treatment, and more pronouncedly after 20 h. A high yield of free cell wall material could be demonstrated after 2 h of penicillin treatment. This corresponded well to an increased content of free endotoxin in the filtrates from the cell cultures treated with penicillin, compared to untreated controls. After 20 h of treatment, free cell wall material had formed large aggregates or was adherent to the cell walls of ghost cells. The corresponding endotoxin analysis showed a reduced content of filtrable endotoxin. Possible implications of the structural changes in relation to penicillin treatment of patients are discussed.

Loss of sulfonamide resistance in Neisseria meningitidis

Four strains of Neisseria meningitidis were studied during serial passage. From two strains which originally were sulfonamide resistant, variants developed that had altered susceptibility to sulfonamides. One of the variants became relatively highly sulfonamide-sensitive, the other exhibited merely reduced sulfonamide resistance. There was a difference in the resistance pattern for two sulfonamides (sulfaisodimidine and sulfamethoxazole), and the effect of inoculum size and growth conditions in three different media could be demonstrated. Although the patterns of susceptibility to other antibacterial agents were different for the strains studied, no further susceptibility alterations occurred in parallel to the sulfonamide sensitivity changes. The variants also lost their ability to liberate free endotoxin.

Loss of endotoxin liberation in Neisseria meningitidis

Four strains of Neisseria meningitidis were studied during serial passage. Upon subcultivation, two of them lost the ability to liberate endotoxin. Ultrastructurally, the two parent endotoxin liberating strains exhibited quantitatively more free cell wall membranes and blebs in the medium than their non-liberating variants. Similarly, the endotoxin-releasing original strains exhibited higher sulfonamide resistance than their variants, and had markedly more sticky cells, which showed pronounced adherence to the surfaces of plastic and heated blood agar.

The endotoxin-liberating effect of antibiotics on meningococci in vitro

Three strains of Neisseria meningitis (two endotoxin-liberating and one in vitro variant non-liberating) were studied during treatment with MIC and 100 times MIC values of benzylpenicillin and chloramphenicol in a chemically-defined, protein-free medium. Treatment with the highest dose of benzylpenicillin had the most rapid effect on meningococci, although the antibacterial effect was the same for the two penicillin concentrations after 20 h. Chloramphenicol treatment showed a much slower antibacterial effect. After 2 h of antibacterial treatment, an increase of filtrable endotoxin in the medium was found for the endotoxin-ligerating strains only when the highest penicillin dose was used. During the same period there was a rapid cell death. After 20 hours of treatment, however, the endotoxin-liberating strains treated with high and low concentrations of penicillin had a markedly reduced content of filtrable endotoxin, compared to the controls and to the cultures treated with chloramphenicol. Antibacterial treatment had no, or only minimal, effect on the total content of endotoxin in the cultures, compared to the untreated controls. The endotoxin non-liberating strain had about the same total content of endotoxin as the liberating strains, but did not liberate filtrable endotoxin into the medium unless filtered with a much higher pressure through a filter with smaller pore size.