Does eradication of meningococcal carriage in household contacts prevent secondary cases of meningococcal disease?

Prevalence and persistence of Neisseria meningitidis carriage in Swedish university students

The bacterium Neisseria meningitidis causes life-threatening disease worldwide, typically with a clinical presentation of sepsis or meningitis, but can be carried asymptomatically as part of the normal human oropharyngeal microbiota. The aim of this study was to examine N. meningitidis carriage with regard to prevalence, risk factors for carriage, distribution of meningococcal lineages and persistence of meningococcal carriage. Throat samples and data from a self-reported questionnaire were obtained from 2744 university students (median age: 23 years) at a university in Sweden on four occasions during a 12-month period. Meningococcal isolates were characterised using whole-genome sequencing. The carriage rate among the students was 9.1% (319/3488; 95% CI 8.2-10.1). Factors associated with higher carriage rate were age ≤22 years, previous tonsillectomy, cigarette smoking, drinking alcohol and attending parties, pubs and clubs. Female gender and sharing a household with children aged 0-9 years were associated with lower carriage. The most frequent genogroups were capsule null locus (cnl), group B and group Y and the most commonly identified clonal complexes (cc) were cc198 and cc23. Persistent carriage with the same meningococcal strain for 12 months was observed in two students. Follow-up times exceeding 12 months are recommended for future studies investigating long-term carriage of N. meningitidis.

[Meningococcal vaccines. Global epidemiological situation and strategies for prevention by vaccination]

N. meningitidis is a major cause of meningitis and septicemia and a major public health problem in many countries. The disease, that can be fulminant, has a high mortality and may cause serious sequelae, even in cases of apparently optimal medical treatment. Chemoprophylaxis may prevent secondary cases among those in close contact with the ill, but, since secondary cases represent only 1%-2% of all meningococcal disease, chemoprophylaxis has a small impact when fighting most of endemic and epidemic forms. Given that al least 5% -15% of children and young adults are carriers, the fight against meningococcal disease based on chemotherapeutic elimination of nasopharyngeal colonization is virtually impossible. Therefore, immunization is the only rational way to combat this disease.

Preventing secondary cases of invasive meningococcal capsular group B (MenB) disease using a recently-licensed, multi-component, protein-based vaccine (Bexsero(®))

OBJECTIVES

To assess the potential use of a protein-based meningococcal group B (MenB) vaccine (Bexsero(®)) in addition to antibiotic chemoprophylaxis for preventing secondary cases.

METHODS

Published studies on the risk of secondary meningococcal infections were used to estimate the numbers needed to vaccinate (NNV) with Bexsero(®) to prevent a secondary case in household and educational settings.

RESULTS

Most secondary cases occur within a few days of diagnosis in the index case. Unlike conjugate vaccines, early protection offered after a single dose of Bexsero(®) is likely to be low, particularly in young children, who are at higher risk of secondary infection. NNV was dependent on predicted meningococcal strain coverage, estimated onset of protection after one Bexsero(®) dose and estimated vaccine efficacy. Even in the most favourable scenario where we assume the vaccine is administered within 4 days of the index case and prevents 90% of cases occurring after 14 days, the NNV for household contacts was >1000. NNV in educational settings was much higher.

CONCLUSIONS

The estimated NNV should be taken into account when deciding policy to recommend Bexsero(®) for close contacts of single cases in household or educational settings. Bexsero(®) may have a protective role in clusters and outbreaks.

Effectiveness of vaccinating household contacts in addition to chemoprophylaxis after a case of meningococcal disease: a systematic review

SUMMARYWe performed a systematic review to estimate the effectiveness of vaccination, in addition to chemoprophylaxis, in preventing meningococcal disease among household contacts. Medline, EMBASE, EMGM, and EUIBIS were used for data collection. Studies reporting on at least 100 primary cases and on subsequent cases in household settings with follow-up of more than 2 weeks after onset of disease in the primary case were reviewed. A meta-analysis was used to calculate the average attack rate in household contacts given chemoprophylaxis 14-365 days after onset of disease in the primary case. In total, 652 studies were identified, five studies and one unpublished report met the inclusion criteria. The weighted average attack rate was 1.1/1000 household contacts (95% CI 0.7-1.7). This review supports vaccination of household contacts in addition to chemoprophylaxis to reduce the risk of meningococcal disease among household contacts of a case caused by a vaccine-preventable serogroup.

Diversity in pathogenicity can cause outbreaks of meningococcal disease

Neisseria meningitidis, the meningococcus, is a major cause of bacterial meningitis and septicemia worldwide. Infection in most cases leads to asymptomatic carriage and only rarely to disease. Meningococcal disease often occurs in outbreaks, which are both sporadic and highly unpredictable. The occurrence of disease outbreaks in a host population in which the etiological agent is widely carried is not well understood. A potential explanation lies in the fact that meningococci are diverse with respect to disease-causing potential. We formulated a stochastic mathematical model to investigate whether diversity of the bacterial population is related to outbreaks of meningococcal disease. In the model, strains that occasionally cause the disease appear repeatedly in a population dominated by a nonpathogenic strain. When the pathogenicity, i.e., the disease-causing potential, of the pathogenic lineage was low, the model shows distinct outbreaks, the size distribution of the outbreaks follows a power law, and the ratio of the variance to the mean number of cases is high. Analysis of notification data of meningococcal disease showed that the ratio of the variance to the mean was significantly higher for meningococcal diseases than for other bacterial invasive diseases. This result lends support to the hypothesis that outbreaks of meningococcal disease are caused by diversity in the pathogenicity of meningococcal strains.

Effectiveness of antibiotics in preventing meningococcal disease after a case: systematic review

OBJECTIVE

To summarise the evidence for the role of antibiotics in preventing further cases of meningococcal disease through chemoprophylaxis given to the index patient, household contacts, and children in day care settings after a single case.

DESIGN

Systematic review.

METHODS

Studies were identified by searching Embase (1983-2003), Medline (1965-2003), and CAB Health (1973-2003) and by contacting the World Health Organization and the European meningococcal disease surveillance network and examining references of identified papers. The review included all studies with at least 10 cases in which outcomes were compared between treated and untreated groups.

MAIN OUTCOME MEASURE

Subsequent cases of meningococcal disease 1-30 days after onset of disease in the index patient.

RESULTS

Four observational studies and one small trial met the inclusion criteria. Meta-analysis of studies on chemoprophylaxis given to household contacts showed a significant reduction in risk (risk ratio 0.11, 95% confidence interval 0.02 to 0.58). The number needed to treat to prevent a case was estimated as 218 (121 to 1135). Primary outcome data were not available in studies of chemoprophylaxis given to the index patient: when prophylaxis had not been given, rate of carriage after discharge from hospital was estimated as 3% (0 to 6), probably an underestimate of the true rate. No studies of chemoprophylaxis in day care settings were identified that met the inclusion criteria.

CONCLUSION

There have been no high quality experimental trials looking at control policies for meningococcal disease. The best available evidence is from retrospective studies. The risk of meningococcal disease in household contacts of a patient can be reduced by an estimated 89% if they take antibiotics known to eradicate meningococcal carriage. Chemoprophylaxis should be recommended for the index patient and all household contacts.

Variations in chemoprophylaxis for meningococcal disease: a retrospective case note review, analysis of routine prescribing data and questionnaire of general practitioners

BACKGROUND

Invasive meningococcal disease is a significant cause of mortality and morbidity in the UK. Administration of chemoprophylaxis to close contacts reduces the risk of a secondary case. However, unnecessary chemoprophylaxis may be associated with adverse reactions, increased antibiotic resistance and removal of organisms, such as Neisseria lactamica, which help to protect against meningococcal disease. Limited evidence exists to suggest that overuse of chemoprophylaxis may occur. This study aimed to evaluate prescribing of chemoprophylaxis for contacts of meningococcal disease by general practitioners and hospital staff.

METHODS

Retrospective case note review of cases of meningococcal disease was conducted in one health district from 1st September 1997 to 31st August 1999. Routine hospital and general practitioner prescribing data was searched for chemoprophylactic prescriptions of rifampicin and ciprofloxacin. A questionnaire of general practitioners was undertaken to obtain more detailed information.

RESULTS

Prescribing by hospital doctors was in line with recommendations by the Consultant for Communicable Disease Control. General practitioners prescribed 118% more chemoprophylaxis than was recommended. Size of practice and training status did not affect the level of additional prescribing, but there were significant differences by geographical area. The highest levels of prescribing occurred in areas with high disease rates and associated publicity. However, some true close contacts did not appear to receive prophylaxis.

CONCLUSIONS

Receipt of chemoprophylaxis is affected by a series of patient, doctor and community interactions. High publicity appears to increase demand for prophylaxis. Some true contacts do not receive appropriate chemoprophylaxis and are left at an unnecessarily increased risk.

[Meningococcal purpura fulminans: untoward result of genetic polymorphism?]

Despite significant progress in intensive care medicine, the mortality of septic shock has not changed in recent years. Early recognition of subtle signs in favor of meningococcal sepsis, early antibiotic treatment, and aggressive hemodynamic support remains the cornerstone of therapy of severe meningococcal shock in children. Recent work has emphasized the role of genetic polymorphisms in various systems to explain the most severe cases: anti-inflammatory cytokine profile IL-10/TNF-alpha, elevated levels of plasminogen activator inhibitor type-1, variants of the gene for mannose-binding lectin complement pathway. This may explain the disillusionment of pediatric intensivists, and the general failure of immunotherapy for sepsis. Reasonable hope lies upon new meningococcal vaccines.

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.

Control of group C meningococcal disease in Australian aboriginal children by mass rifampicin chemoprophylaxis and vaccination

An outbreak of 12 cases of meningitis, 11 caused by Neisseria meningitidis serogroup C, occurred at Doomadgee from September, 1990, to April, 1991. The incidence of meningitis was 17.55/10(3) person-years. Only children aged 1-10 years were affected. In October, 1990, or shortly thereafter, 473/509 children aged between 1 and 15 years inclusive had one dose of Mencevax AC. From the time of vaccination until April, 1991, a further eight cases occurred, six in vaccinated children. Vaccine efficacy in 1-15 year olds was calculated as 77%. Despite this, in April, 1991, the prevalence of antibody to group C polysaccharide in vaccinated children (78%) was not significantly different from that in unvaccinated children and adults. 46 nonresponders were revaccinated, and, in February, 1992, 78% had antibodies to group C polysaccharide. In April, 1991, an estimated 3.0% of the population had group C organisms, carriage being directly related to household crowding. In June, 1991, 2 months after mass prophylaxis with rifampicin, none of these individuals were carriers. In October, 1991, the carriage rate of group C organisms was 0.64%. There have been no further cases caused by the epidemic strain. Although uncrowded housing is a basic need, mass chemoprophylaxis and two doses of vaccine for children should be used in similar outbreaks.

Smoking, the environment and meningococcal disease: a case control study

This case control study investigated environmental factors in 74 confirmed cases of meningococcal disease (MD). In children aged under 5, passive smoking in the home (30 or more cigarettes daily) was associated with an odds ratio (OR) of 7.5 (95% confidence interval (CI) 1.46-38.66). ORs increased both with the numbers of cigarettes smoked and with the number of smokers in the household, suggesting a dose-response relationship. MD in this age group was also significantly associated with household overcrowding (more than 1.5 persons per room) (OR 6.0, 95% CI 1.10-32.8), with kisses on the mouth with 4 or more contacts in the previous 2 weeks (OR 2.46, 95% CI 1.09-5.56), with exposure to dust from plaster, brick or stone in the previous 2 weeks (OR 2.24, 95% CI 1.07-4.65); and with changes in residence (OR 3.0, 95% CI 1.0-8.99), marital arguments (OR 3.0, 95% CI 1.26-7.17) and legal disputes in the previous 6 months (OR 3.10, 95% CI 1.24-7.78). These associations were independent of social class. Public health measures to lower the prevalence of cigarette smoking by parents of young children may reduce the incidence of MD. The influence of building dust and stressful life events merits further investigation.

Asymptomatic carriage of Neisseria meningitidis in a randomly sampled population

To estimate the extent of meningococcal carriage in the Norwegian population and to investigate the relationship of several characteristics of the population to the carrier state, 1,500 individuals living in rural and small-town areas near Oslo were selected at random from the Norwegian National Population Registry. These persons were asked to complete a questionnaire and to volunteer for a bacteriological tonsillopharyngeal swab sampling. Sixty-three percent of the selected persons participated in the survey. Ninety-one (9.6%) of the volunteers harbored Neisseria meningitidis. The isolates were serogrouped, serotyped, tested for antibiotic resistance, and analyzed by multilocus enzyme electrophoresis. Eight (8.8%) of the 91 isolates represented clones of the two clone complexes that have been responsible for most of the systemic meningococal disease in Norway in the 1980s. Age between 15 and 24, male sex, and active and passive smoking were found to be independently associated with meningococcal carriage in logistic regression analyses. Working outside the home and having an occupation in transportation or industry also increased the risk for meningococcal carriage in individuals older than 17, when corrections for gender and smoking were made. Assuming that our sample is representative of the Norwegian population, we estimated that about 40,000 individuals in Norway are asymptomatic carriers of isolates with epidemic potential. Thus, carriage eradication among close contacts of persons with systemic disease is unlikely to have a significant impact on the overall epidemiological situation.

Transmission of Neisseria meningitidis among asymptomatic military recruits and antibody analysis

Following the occurrence of a case of systemic meningococcal disease in a military camp in Norway, throat cultures and blood samples were collected from 33 healthy individuals belonging to the same troop as the patient (troop A) and from 29 individuals from a different troop (troop B) in the same camp. Serological studies showed that 91% of the recruits had bactericidal antibodies against the disease-causing strain. The isolates of Neisseria meningitidis recovered from the throat cultures were serogrouped, serotyped, and assigned to a clone on the basis of an analysis of the electrophoretic mobilities of 14 metabolic enzymes. None of the 23 carriers in troop A harboured the clone responsible for the case of disease, but 6 carried isolates of the same electrophoretic type, ET-7, which was not identified in any of the 19 carriers of troop B. Individuals in troop A were resampled 2 and 17 weeks after the meningococcal disease episode. Five of the carriers had acquired different clones and one of them changed clone twice in that period. Four of the six newly acquired clones had previously been identified in other carriers of troop A, demonstrating transmission of clones among individuals living and working in close proximity.

Preventing secondary cases of meningococcal disease by identifying and eradicating disease-causing strains in close contacts of patients

In Norway, the use of chemoprophylaxis after cases of meningococcal disease is not recommended. Instead, household members less than 15 years are treated with penicillin for 7 days. Failures of this treatment have been reported. We therefore used DNA fingerprinting to identify the disease-causing strain in healthy contacts combined with selective rifampicin prophylaxis to these carriers to prevent secondary cases. During a 2-year period (1987-89) there were 13 cases of meningococcal disease in the County of Telemark (165000 inhabitants). 65 (14.7%) out of 441 contacts to these 13 patients harbored meningococci in their throat; 16 (3.6%) carried the disease-causing strain. Only 1 carrier fulfilled the criteria for being treated with penicillin; 8 were adults and the remaining 7 were not household members. No secondary cases of meningococcal disease occurred during the study period or the following 12 months. During the 4-year period (1984-87) preceding the study period there were 39 cases of meningococcal disease in Telemark; 7 of them were index cases for 12 bacteriologically verified and 4 clinically suspected secondary cases of meningococcal disease. We conclude that selective prophylaxis with rifampicin seems to be more efficient that penicillin treatment of household members less than 15 to prevent secondary cases of meningococcal disease.

Meningococcal carriage in close contacts of cases

Between 1 October 1986 and 31 March 1987, 55 cases of meningococcal disease were identified in the South-West of England, an attack rate of 1.54 per 100,000 during the study period. Antibiotics used in the treatment of the disease successfully eliminated nasopharyngeal carriage of meningococci in 13 out of 14 cases without use of rifampicin. The overall meningococcal carriage rate in 384 close contacts was 18.2% and the carriage rate of strains indistinguishable from the associated case strain was 11.1%. The carriage rate of indistinguishable strains in household contacts (16.0%) was higher than the carriage rate in contacts living at other addresses (7.0%, P less than 0.05). A 2-day course of rifampicin successfully eradicated meningococci from 46 (98%) of 47 colonized contacts. In one third of cases groupable meningococci were isolated from at least one household contact; 92% of these isolates were of the same serogroup as the associated case strain. When a meningococcus is not isolated from a deep site in a clinical case of meningococcal disease, culture of serogroup A or C strains from nasopharyngeal swabs of the case or of household contacts is an indication that the close contact group should be offered meningococcal A + C vaccine in addition to chemoprophylaxis. The failure in this and other studies to isolate meningococci from any household contact in the majority of cases may be due either to the relative insensitivity of nasopharyngeal swabbing in detecting meningococcal carriage or to the acquisition of meningococci by most index cases from sources outside the household.

Epidemiology of meningococcal disease in Denmark 1980-1988

Based on epidemiological data of notified cases of meningococcal disease (MD) in Denmark during the period 1980-88 the recommendations for prophylaxis are evaluated. In 1986 the incidence of MD increased about 60% to 5.5 per 100,000 population. The clinical diagnosis of MD was verified by culture of Neisseria meningitidis in 79% of notified cases. About 40% of all patients were less than 4 years of age. The mortality in 1988 was found to be 10%. Serogroup B disease accounted for about 80% of the cases. Two co-primary and 28 secondary cases were registered. Two major outbreaks of serogroup C disease occurred in 1984 and 1986, respectively. In small clusters of 2-3 cases within socially well-defined groups the recommendations for prophylaxis are sufficient. But for the new pattern of clusters spread over months to years in certain geographical areas or open social groups, especially among teenagers, the existing recommendations are insufficient. The occurrence of localized clusters of serogroup B disease emphasises the need for a vaccine against serogroup B disease.