Clinical and laboratory diagnosis of pertussis in the regions of a large vaccine efficacy trial in Germany

Pharmacotherapy for Bordetella pertussis infection. II. A synthesis of clinical sciences

Despite the plethora of studies that have examined laboratory susceptibility testing for Bordetella pertussis, assessments of treatment have lagged far behind both in quality and quantity. Macrolides and trimethoprim/sulfamethoxazole historically served the needs of both treatment and prevention, albeit there is still controversy about the degree of protection measured both bacteriologically and clinically. As high-level macrolide resistance has emerged in some geographic regions and since macrolides have been the mainstay of therapy, alternative antibiotics need to be defined for pertussis. In vitro susceptibility testing suggests the potential for several alternatives to macrolides, including trimethoprim/sulfamethoxazole, specific β-lactam agents, chloramphenicol, some quinolones and possibly some tetracyclines. For the latter antibiotics, more clinical studies for treatment and prophylaxis are required in to order to establish bacteriological-clinical correlates for outcome. In the interim, if the clinical circumstances mandate the use of proposed interim alternatives to macrolides, outcomes should be assessed with test of cure by culture, since genetic amplification technologies do not discriminate bacterial viability. Whereas there may be debate in regard to using placebo or macrolides as the controls for alternative antibiotic therapy in geographies where most B. pertussis isolates are antibiotic-susceptible, both placebo and macrolide controls should be assessed along with alternative antibiotics in well-designed controlled studies in regions pressured by macrolide resistance. Outcomes of clinical response and epidemiological patterns of disease should continue to be monitored given the degree of macrolide resistance that is emerging.

Bordetella pertussis

Pertussis is a highly infectious vaccine-preventable cough illness that continues to be a significant source of morbidity and mortality around the world. The majority of human illness is caused by Bordetella pertussis, and some is caused by Bordetella parapertussis. Bordetella is a Gram-negative, pleomorphic, aerobic coccobacillus. In the past several years, even countries with high immunization rates in early childhood have experienced rises in pertussis cases. Reasons for the resurgence of reported pertussis may include molecular changes in the organism and increased awareness and diagnostic capabilities, as well as lessened vaccine efficacy and waning immunity. The most morbidity and mortality with pertussis infection is seen in infants too young to benefit from immunization. Severe infection requiring hospitalization, including in an intensive care setting, is mostly seen in those under 3 months of age. As a result, research and public health actions have been aimed at better understanding and reducing the spread of Bordetella pertussis. Studies comparing the cost benefit of cocooning strategies versus immunization of pregnant women have been favorable towards immunizing pregnant women. This strategy is expected to prevent a larger number of pertussis cases, hospitalizations, and deaths in infants <1 year old while also being cost-effective. Studies have demonstrated that the source of infection in infants usually is a family member. Efforts to immunize children and adults, in particular pregnant women, need to remain strong.

Clinical Characteristics of Pertussis-Associated Cough in Adults and Children: A Diagnostic Systematic Review and Meta-Analysis

BACKGROUND

Pertussis (whooping cough) is a highly infective cause of cough that causes significant morbidity and mortality. Existing case definitions include paroxysmal cough, whooping, and posttussive vomiting, but diagnosis can be difficult. We determined the diagnostic accuracy of clinical characteristics of pertussis-associated cough.

METHODS

We systematically searched CINAHL, Embase, Medline, and SCI-EXPANDED/CPCI-S up to June 2016. Eligible studies compared clinical characteristics in those positive and negative for Bordetella pertussis infection, confirmed by laboratory investigations. Two authors independently completed screening, data extraction, and quality and bias assessments. For each characteristic, RevMan was used to produce descriptive forest plots. The bivariate meta-analysis method was used to generate pooled estimates of sensitivity and specificity.

RESULTS

Of 1,969 identified papers, 53 were included. Forty-one clinical characteristics were assessed for diagnostic accuracy. In adult patients, paroxysmal cough and absence of fever have a high sensitivity (93.2% [CI, 83.2-97.4] and 81.8% [CI, 72.2-88.7], respectively) and low specificity (20.6% [CI, 14.7-28.1] and 18.8% [CI, 8.1-37.9]), whereas posttussive vomiting and whooping have low sensitivity (32.5% [CI, 24.5-41.6] and 29.8% [CI, 8.0-45.2]) and high specificity (77.7% [CI, 73.1-81.7] and 79.5% [CI, 69.4-86.9]). Posttussive vomiting in children is moderately sensitive (60.0% [CI, 40.3-77.0]) and specific (66.0% [CI, 52.5-77.3]).

CONCLUSIONS

In adult patients, the presence of whooping or posttussive vomiting should rule in a possible diagnosis of pertussis, whereas the lack of a paroxysmal cough or the presence of fever should rule it out. In children, posttussive vomiting is much less helpful as a clinical diagnostic test.

Clinical presentation and microbiological diagnosis in paediatric respiratory tract infection: a systematic review

BACKGROUND

Antibiotic prescribing decisions for respiratory tract infection (RTI) in primary care could be improved if clinicians could target bacterial infections. However, there are currently no evidence-based diagnostic rules to identify microbial aetiology in children presenting with acute RTIs.

AIM

To analyse evidence of associations between clinical symptoms or signs and detection of microbes from the upper respiratory tract (URT) of children with acute cough.

DESIGN AND SETTING

Systematic review and meta-analysis.

METHOD

A literature search identified articles reporting relationships between individual symptoms and/or signs, and microbes detected from URT samples. Associations between pathogens and symptoms or signs were summarised, and meta-analysis conducted where possible.

RESULTS

There were 9984 articles identified, of which 28 met inclusion criteria. Studies identified 30 symptoms and 41 signs for 23 microbes, yielding 1704 potential associations, of which only 226 (13%) have presently been investigated. Of these, relevant statistical analyses were presented for 175 associations, of which 25% were significant. Meta-analysis demonstrated significant relationships between respiratory syncytial virus (RSV) detection and chest retractions (pooled odds ratio [OR] 1.9, 95% confidence interval [CI] = 1.6 to 2.3), wheeze (pooled OR 1.7, 95% CI = 1.5 to 2.0), and crepitations/crackles (pooled OR 1.7, 95% CI = 1.3 to 2.2).

CONCLUSIONS

There was an absence of evidence for URT pathogens other than RSV. The meta-analysis identified clinical signs associated with RSV detection, suggesting clinical presentation may offer some, albeit poor, diagnostic value. Further research is urgently needed to establish the value of symptoms and signs in determining microbiological aetiology and improve targeting of antibiotics in primary care.

Clinical and laboratory features of pertussis in hospitalized infants with confirmed versus probable pertussis cases

BACKGROUND

The clinical presentations of pertussis infection have considerable variation. Many infections and illnesses can cause prolonged repetitive paroxysmal cough that could be confused with Bordetella pertussis infection.

AIM

This retrospective study was designed to compare the clinico-laboratory findings between two groups of hospitalized infants with confirmed, and those who have clinical pertussis disease; to identify the possible additional diagnostic clues "for the diagnosis of confirmed pertussis disease".

SUBJECTS AND METHODS

The study population consisted of infants ≤12 months of age with clinical diagnosis of pertussis that fulfilled the World Health Organization definition for pertussis or those diagnosed by physicians. Clinico-laboratory findings were compared between two groups of patients (confirmed vs. clinical cases).

RESULTS

From a total of 118 infants admitted with a clinical diagnosis of pertussis, 16% (19/118) were confirmed by laboratory to have confirmed pertussis. Twelve of 19 (63%) and 71.99% of confirmed and clinical cases were younger than 6 months of age, respectively. For most patients, the duration of symptoms before hospitalization was <14 days. There were no significant differences between two groups of patients for paroxysmal cough and facial discoloration. However, whoop and apnea were more common among confirmed pertussis cases: P = 0.01, and P = 0.02, respectively. Leukocytosis (≥16,000/ml) (P = 0.01) and lymphocytosis (≥11,000) (P = 0.02) were reported significantly more frequently in confirmed pertussis cases.

CONCLUSION

Given the unavailability of a highly sensitive diagnostic test, in every afebrile patient with paroxysmal cough lasting for ≥7 days associated with whoop and/or apnea, particularly if accompanied by leukocytosis/lymphocytosis, pertussis disease should be considered. In this situation, prompt administration of empiric treatment for cases, and providing control measures to prevent infection transmission to contacts are recommended.

Diagnosis of pertussis: a historical review and recent developments

The accurate and timely diagnosis of pertussis continues to be challenging. The widespread use of pertussis vaccines has dramatically altered the epidemiology and clinical presentation of pertussis disease, such that many cases do not present with the hallmark symptoms, such as inspiratory whoop, post-tussive vomiting and paroxysmal cough. A variety of laboratory tools are available to aid in the diagnosis of pertussis, including culture, direct fluorescent antibody testing, PCR, and paired and single serology techniques. This article reviews the strengths and limitations, including the sensitivity and specificity, of each of these diagnostic tools.

Seroprevalence of Bordetella pertussis antibody in children and adolescents in China

BACKGROUND

This multicenter study was undertaken to investigate the serologic evidence of antibodies to Bordetella pertussis toxin (IgG-PT) in children and adolescents.

METHODS

IgG-PT value in a single serum collected from 1616 children and adolescents was measured by enzyme-linked immunosorbent assay in the Food and Drug Administration (FDA)-units per milliliter from November 2008 to October 2009. The relationship between time since infection and IgG anti-PT levels were analyzed and the estimated age-specific incidences of infection were calculated.

RESULTS

The sera IgG-PT geometric mean concentrations of the samples were 1.7 FDA-U/mL. The sera protective rates of all the subjects were 6.6% (95% confidential interval [CI]: 5.4%, 7.8%). The rates in the group aged 2 years was 9.2% (95% CI: 3.5%, 14.9%), which was significantly higher than in those aged ≥ 3 years (χ = 1615, P = 0.000). In the group aged ≥ 3 years, 4.0% (95% CI: 3.0%, 5.0%) of the individuals tested showed an IgG-PT level ≥ 40 FDA-U/mL, which was equivalent to an estimated incidence of B. pertussis infection of 7000 (95% CI: 5300, 8800) per 100,000 population per year in the year before serum sampling. There were 2 peaks of estimated incidence. One peak incidence of 9100 (95% CI: 4300, 14000) per 100,000 population per year was found in the population aged >6 to 8 years. Another peak was in the population of 12- to 20-year olds with the estimated incidence of 14,600 (95% CI: 9100, 20100) per 100,000 per year.

CONCLUSIONS

The levels of protective antibodies against pertussis were very low in the immunized children aged 2 to 20 years. A booster dose of immunization for older children or adolescents should be an urgent priority. Moreover, using enzyme-linked immunosorbent assay to determine the efficiency of vaccines and even to obtain the serodiagnosis would be beneficial in controlling pertussis.

Pertussis immunisation in adolescents and adults –Bordetella pertussisepidemiology should guide vaccination recommendations

Pertussis, or whooping cough, is an infectious disease that is caused by Bordetella pertussis, affects all age groups and is vaccine preventable. Recently, an increase in reported cases of pertussis in adolescents and adults has been noted in many countries despite high immunisation rates in children. Today pertussis outnumbers all other paediatric vaccine-preventable diseases in some countries. This observation can best be explained by an increased awareness of the disease, the availability of new diagnostic tests and, perhaps, suboptimal efficacy of some pertussis vaccines. In general, B. pertussis infections in adolescents and adults are of concern as they are the most important source of transmission of B. pertussis infections to young, unprotected infants. Many studies with diphtheria and tetanus toxoid, acellular pertussis component combination vaccines, specifically designed for use in adolescents and adults, have been performed and excellent tolerability and immunogenicity have been demonstrated. With the availability of two such products, booster doses in adolescents have been introduced in Canada, Austria, Australia, France, Germany and the US, and many other countries are considering similar expansion of their immunisation programmes at present. In addition, universal immunisation of adults (Austria, every 10 years) or targeting high risk groups (e.g., parents of newborns and other care-givers to children; Germany) have been recommended. If lifelong regular booster doses against pertussis were to be recommended and universal implementation was obtained, the authors believe that the morbidity of pertussis and its spread to infants can be dramatically reduced, and it is possible that the circulation of B. pertussis could be eliminated.

Recent developments in pertussis

Pertussis causes nearly 300,000 deaths in children every year. Most deaths take place in developing countries, but the infection remains a priority everywhere. Pertussis vaccination protects infants and children against death and admission to hospital, but breakthrough disease in vaccinated people can happen. In high-mortality countries, the challenge is to improve timeliness and coverage of childhood vaccination and surveillance. In regions with low mortality and highest coverage, pertussis is frequently the least well-controlled disease in childhood vaccination programmes. Some countries have reported a rise in pertussis in adolescents, adults, and pre-vaccination infants, but how much these changes are real or a result of improved recognition and surveillance remains uncertain. In response, several countries have introduced adolescent and adult acellular pertussis vaccine boosters. The effect so far is unknown; assessment is impeded by poor data. Uncertainties still persist about key variables needed to model and design vaccination programmes, such as risk of transmission from adults and adolescents to infants. New vaccination strategies under investigation include vaccination of neonates, family members, and pregnant women.

Efficacy of an acellular pertussis vaccine among adolescents and adults

BACKGROUND

Pertussis immunization of adults may be necessary to improve the control of a rising burden of disease and infection. This trial of an acellular pertussis vaccine among adolescents and adults evaluated the incidence of pertussis, vaccine safety, immunogenicity, and protective efficacy.

METHODS

Bordetella pertussis infections and illnesses were prospectively assessed in 2781 healthy subjects between the ages of 15 and 65 years who were enrolled in a national multicenter, randomized, double-blind trial of an acellular pertussis vaccine. Subjects received either a dose of a tricomponent acellular pertussis vaccine or a hepatitis A vaccine (control) and were monitored for 2.5 years for illnesses with cough that lasted for more than 5 days. Each illness was evaluated with use of a nasopharyngeal aspirate for culture and polymerase-chain-reaction assay, and serum samples from patients in both acute and convalescent stages of illness were analyzed for changes in antibodies to nine B. pertussis antigens.

RESULTS

Of the 2781 subjects, 1391 received the acellular pertussis vaccine and 1390 received the control vaccine. The groups had similar ages and demographic characteristics, and the median duration of follow-up was 22 months. The acellular pertussis vaccine was safe and immunogenic. There were 2672 prolonged illnesses with cough, but the incidence of this nonspecific outcome did not vary between the groups, even when stratified according to age, season, and duration of cough. On the basis of the primary pertussis case definition, vaccine protection was 92 percent (95 percent confidence interval, 32 to 99 percent). Among unimmunized controls with illness, 0.7 percent to 5.7 percent had B. pertussis infection, and the percentage increased with the duration of cough. On the basis of other case definitions, the incidence of pertussis in the controls ranged from 370 to 450 cases per 100,000 person-years.

CONCLUSIONS

The acellular pertussis vaccine was protective among adolescents and adults, and its routine use might reduce the overall disease burden and transmission to children.

Defining pertussis epidemiology: clinical, microbiologic and serologic perspectives

In the past decade, numerous sources have noted an increase in reported pertussis in highly immunized populations. This has been accompanied by a perceived change in disease epidemiology, characterized by a significant increase in reported pertussis incidence among adolescents and adults. In populations where children are routinely immunized, adolescents and adults now constitute the main source of infection in infants. However, a range of factors makes delineation of these epidemiologic trends difficult. Reported cases of pertussis represent only a fraction of the actual number of Bordetella pertussis symptomatic infections, because underconsulting, underrecognition and underdiagnosis are widespread and are a particular problem in adolescents and adults. Possible explanations for failure to diagnose pertussis include the heterogeneity in pertussis disease expression and low physician awareness and index of suspicion. Consequently defining pertussis from a clinical perspective is difficult, and this is reflected by a lack of consistency between case definitions. Although case definitions for specific circumstances have been established by the World Health Organization and the United States Centers for Disease Control, these are not universally useful, making intercountry comparisons and global evaluation difficult. Less-than-optimal and poorly performed laboratory tests, or their lack of availability, also make confirmation of B. pertussis infection difficult. To overcome these problems, clinical case definitions should be standardized for outbreak and endemic situations. Rapid, easy-to-use and inexpensive laboratory diagnostic techniques also must be made available and be widely implemented. In particular, polymerase chain reaction and single serum serology are 2 techniques that should be more widely adopted.

Molecular pathogenesis, epidemiology, and clinical manifestations of respiratory infections due to Bordetella pertussis and other Bordetella subspecies

Bordetella respiratory infections are common in people (B. pertussis) and in animals (B. bronchiseptica). During the last two decades, much has been learned about the virulence determinants, pathogenesis, and immunity of Bordetella. Clinically, the full spectrum of disease due to B. pertussis infection is now understood, and infections in adolescents and adults are recognized as the reservoir for cyclic outbreaks of disease. DTaP vaccines, which are less reactogenic than DTP vaccines, are now in general use in many developed countries, and it is expected that the expansion of their use to adolescents and adults will have a significant impact on reducing pertussis and perhaps decrease the circulation of B. pertussis. Future studies should seek to determine the cause of the unique cough which is associated with Bordetella respiratory infections. It is also hoped that data gathered from molecular Bordetella research will lead to a new generation of DTaP vaccines which provide greater efficacy than is provided by today's vaccines.

Comparison of pulsed field gel electrophoresis patterns of Bordetella pertussis isolates from unvaccinated children with severe or mild pertussis

BACKGROUND

The clinical spectrum of pertussis ranges from mild cough illnesses of short duration to typical illness with paroxysmal cough, whooping and posttussive vomiting. We performed comparative genotyping of Bordetella pertussis isolates from children in Germany with severe or mild pertussis.

METHODS

Pulsed field gel electrophoresis (PFGE) of genomic DNA, digested with the restriction endonucleases Xba I and Spe I, was used to determine the profiles of strains isolated from 31 unvaccinated children with severe symptoms of pertussis (with hospitalization and/or complications) compared with isolates from 32 matched children with mild symptoms.

RESULTS

No significant differences in PFGE patterns were found in B. pertussis strains isolated from children with severe vs. mild illness.

CONCLUSIONS

Differences in virulence of circulating B. pertussis strains can be absent or might not correlate with specific PFGE patterns. Other methods should be evaluated to identify differences in virulence.

Determination of pertactin IgG antibodies for the diagnosis of pertussis

OBJECTIVE

To compare increases in serum IgG antibody against pertactin with increases in IgG against pertussis toxin and filamentous hemagglutinin (FHA) in non-vaccinated children, children vaccinated with pertussis toxoid, and adults, all with culture-confirmed pertussis.

METHODS

During a double-blind, placebo-controlled, efficacy trial of a monocomponent pertussis toxoid vaccine, acute and convalescent sera were obtained from study children and family members with suspected pertussis. In the present study, IgG antibodies against pertactin, pertussis toxin and FHA (determined by ELISA) were compared in 207 individuals with culture-verified pertussis and paroxysmal cough for >/= 21 days.

RESULTS

Significant increases in geometric mean serum IgG against all antigens occurred in non-vaccinated children, but more children responded against pertussis toxin and FHA than against pertactin (96%, 97%, and 62%, respectively). Of the children who had pertussis even though they were vaccinated with the pertussis toxoid vaccine, 97% responded to FHA, while responses to pertussis toxin and pertactin were less common (68% and 61%, respectively). In the 20 adults, the proportions of responders to FHA, pertussis toxin and pertactin were 90%, 80% and 55%, respectively.

CONCLUSION

Determination of IgG against pertussis toxin and FHA in paired sera in non-vaccinated children with pertussis is a more sensitive diagnostic tool than determination of IgG against pertactin. Pertactin IgG determinations might be of value as a complement to the other antibody assays in vaccinated children and in adults.

[Culture-confirmed whooping cough in a tertiary center over a twelve-year period]

OBJECTIVE

To study the characteristics of patients diagnosed with whooping cough at a tertiary center in Barcelona, Spain.

MATERIAL AND METHODS

We performed a retrospective study of patients aged less than 18 years treated for pertussis-like cough or clinically-suspected whooping cough over a 12-year period (1989-2000). Only patients with isolated Bordetella spp. were included. The variables of age, sex, vaccination status, hospitalization, clinical manifestations, severity, and lethality were analyzed.

RESULTS

One hundred sixty-one patients with positive Bordetella spp. culture were identified. Of these, complete information was available in 149 (79 boys and 70 girls) with a median age of 3 months (range: 13 days-17 years); 77.2 % were aged 6 months or less. All the isolated strains corresponded to B. pertussis except three that corresponded to B. parapertussis. Three epidemic cycles (in 1989, 1992 and 2000) were observed during the study period. A total of 72.5 % of cases occurred between May and September. Bordetella spp. was associated with other bacteria in 28.2 % of the patients, viruses in 13.4 % and a bacterium and a virus in 4.7 %. One hundred twenty-one patients required hospitalization, of which 14.9 % were admitted to the intensive care unit. Age was the only factor associated with risk for hospitalization, which was more frequent in younger infants (p < 0.0001). Paroxysmal cough with cyanosis was present in 53.4 % of the patients, leucocytosis with lymphocytosis occurred in 67.5 % and apneas were present in 21.5 %. Chest X-ray revealed atelectasis in 34.1 %. The mean length of hospital stay was 11 days (range: 1-70 days). Three boys aged less than 3 months with malignant pertussis syndrome died (lethality: 2 %). More than half the patients (59.7 %) were not vaccinated (55.4 % for being under the age of 3 months) and only 16 % had received three or more vaccination doses.

CONCLUSIONS

Whooping cough continues to be a severe disease in infants, with a high admission rate during the first 6 months of life. New preventive strategies are required to protect infants who have not yet developed full immunity to this infection.

Which strategy for pertussis vaccination today?

Pertussis (whooping cough) remains an epidemic disease responsible for infant and child morbidity and mortality, and is perceived as a serious public health problem. Since the widespread use of whole-cell pertussis vaccines in the 1940s, vaccination programs have varied greatly between countries. National specificity is a function of several factors. The most important are: vaccine efficacy and tolerability;vaccine coverage and distribution; and vaccine acceptance by parents and professionals. During the 1970s, Sweden, England, Wales and Japan provided contrasting examples of the attitude of health authorities to the use of whole-cell vaccines. The increase in pertussis incidence was noted as a consequence of active opposition to this vaccine. The re-emergence of pertussis in the 1990s, in countries with high vaccination coverage and increased incidence of disease in individuals >15 years and <6 months of age, has drawn attention to the role of booster doses of pertussis vaccines and their introduction into regular vaccination programs. The use of acellular vaccines for booster doses for adolescents and adults would seem unambiguous because of their decreased reactogenicity, although the exact schedule has yet to be established. The choice between the two kinds of vaccines is more difficult for primary courses, where safety and efficacy profiles are similar, and the attitude towards acellular vaccines varies from country to country. In this case, the strategy adopted results from the national history of pertussis infection and from the quality of the available whole-cell vaccine. Two contrasting examples are the US, where acellular vaccines were licensed for the primary series in the 1990s, and the UK, where whole-cell vaccines are exclusively used for primary immunization. The changing epidemiology of pertussis, and its local diversification, would suggest that at present it is difficult to define a single worldwide strategy with only one kind of vaccine and one schedule. In order to control pertussis incidence, each country should continue to determine the best national vaccination program established in very close relation to the past and present epidemiological situation and available healthcare resources.

Clinical validation of a polymerase chain reaction assay for the diagnosis of pertussis by comparison with serology, culture, and symptoms during a large pertussis vaccine efficacy trial

OBJECTIVE

To assess the diagnostic sensitivity and specificity of a Bordetella pertussis polymerase chain reaction (PCR) assay using nasopharyngeal (NP) specimens from subjects with cough illnesses participating in a large pertussis vaccine efficacy trial.

DESIGN

From 1991 to 1994, we conducted a large pertussis vaccine efficacy trial in Germany to determine the efficacy of the Lederle/Takeda acellular pertussis component diphtheria-tetanus toxoids in comparison with the Lederle whole-cell component diphtheria-tetanus toxoids vaccine. In the final year of the follow-up period of this trial, a second NP specimen for PCR, in addition to a culture specimen and blood for specific serology (enzyme-linked immunosorbent assay), was collected by use of a Dacron swab in subjects or family members with cough illnesses >/=7 days duration or in subjects with exposure to a cough illness in a household member to establish a diagnosis of B pertussis infection. Oligonucleotide primers (pTp1 and pTp2) that amplify a 191-bp-sized DNA fragment from the pertussis toxin operon, which is specific for B pertussis, were used. The PCR-amplified products were visualized by dot blot analysis followed by hybridization with a digoxigenin labeled probe and rated as 1+, 2+, or 3+ in comparison with positive controls representing approximately 1 to 10, 11 to 50, and >50 B pertussis organisms, respectively. In the present analysis, we compare PCR findings with those of serology, culture, positive household contact, and clinical characteristics of cough illnesses.

RESULTS

Of 392 subjects with NP specimens obtained for PCR, 376 also had NP specimens collected for culture and 282 had serum specimens. PCR and culture were positive in 86 (22%) and 23 (6%) subjects, respectively. Of the positive PCR specimens, 40 were rated 3+, 32 were rated 2+, and 14 were rated 1+; 3+ positive specimens were more prevalent among DT recipients compared with pertussis vaccine recipients. Illnesses in subjects with 3+ positive PCR results were more typical of pertussis than were those in subjects with 2+ and 1+ positive results with a mean duration of cough of 48 days versus 43 and 42 days, respectively; presence of paroxysms, whoop or vomiting in 38% versus 17% and 10%, respectively; and a clinical diagnosis of definite or probable pertussis by the investigators of 26% versus 7% and 4%, respectively. Using serologic evidence of infection as the standard, sensitivity of PCR was 61%, and specificity was 88%. For 3+ positive PCR results, the respective values were 42% and 97%.

CONCLUSION

Our findings demonstrate that PCR is more sensitive than conventional culture for the diagnosis of pertussis. They also demonstrate a high specificity of PCR when serology with or without other confirmative criteria (culture and household contact) is used as the reference. Analysis of semiquantitative PCR results revealed that subjects with a 3+ PCR more frequently experienced typical illness compared with patients with 1+ or 2+ PCR. Although specific serologic study remains a necessity in pertussis research its modification for diagnosis in the clinical setting results in low sensitivity and specificity. Therefore, because PCR is more sensitive than culture and is easy to perform, it is a useful addition in the clinical setting.

A search for serologic correlates of immunity to Bordetella pertussis cough illnesses

In a pertussis vaccine efficacy trial in Germany we collected sera from vaccinees (DTaP or DTP) after the third and fourth doses of vaccine or at comparable time periods in DT vaccine recipients. In addition, sera were collected from a randomized sample of subjects in each vaccine group at approximately 3-month intervals from which antibody kinetic curves were constructed, which allowed us to estimate specific antibody values to pertussis toxin (PT), filamentous hemagglutinin (FHA), pertactin and fimbriae-2 at the time of exposure in the household setting. The imputed geometric mean antibody values to PT, pertactin and fimbriae-2 at the time of household exposure to Bordetella pertussis infection were higher (p < 0.07 or lower) in non-cases compared with cases. A multivariate (classification tree) analysis found that only pertactin and PT were significant in protection. Subjects with an imputed pertactin value of < 7 EU ml-1 had a 67% (18/27) chance of infection regardless of the PT value. If the pertactin value was > or = 7 EU ml-1 and the PT value > or = 66 EU ml-1 all subjects were non-cases. If the pertactin value was > or = 7 and the PT value was < 66 EU ml-1 the predicted probability of being a case was 31% (15/49). Logistic regression analysis also found that high versus low pertactin values were associated with illness prevention following household exposure. In the presence of antibody to pertactin, PT and fimbriae-2, the additional presence of antibody to FHA did not contribute to protection. Our data support historical data indicating that agglutinating antibodies are associated with protection and also recent serologic correlates data and clinical efficacy data which indicate that multicomponent vaccines containing pertactin and fimbriae have better efficacy than PT or PT/FHA vaccines.

The effect of investigator compliance (observer bias) on calculated efficacy in a pertussis vaccine trial

BACKGROUND

In the course of a large pertussis vaccine efficacy trial we realized that investigator compliance could have a major impact on calculated vaccine efficacy.

DESIGN

In our pertussis vaccine efficacy trial, the study investigators were to monitor illness in study families by telephone every 2 weeks. If a cough illness of >/=7 days duration was noted, the study child was to be evaluated. If the cough illness persisted for >/=14 days, the child was to be referred to a central investigator. For this report we analyzed study physician evaluation rates and rates of referral to the central investigators. Physician practices were separated into three compliance categories: high, intermediate, and low. We analyzed vaccine efficacy of an acellular pertussis component DTP vaccine (DTaP) and a whole cell pertussis component DTP vaccine (DTP) by compliance category. Bordetella pertussis infection was documented by culture of the organism in the study child or in a household contact or by a significant antibody response to pertussis toxin determined by enzyme-linked immunosorbent assay.

RESULTS

Using a clinical case definition that included both mild and typical pertussis (cough illness >/=7 days duration) efficacy of DTaP vaccine was 40% (95% confidence interval [CI] = -3-65) in the high compliance category and 78% (95% CI = 65-86) and 75% (95% CI = 53-87) in the intermediate and low compliance groups, respectively. Similar, but less marked, differences in efficacy were noted with DTP vaccine recipients. Using a clinical case definition that required >/=21 days of cough with paroxysms, whoop, or vomiting (typical pertussis) the efficacy of DTaP vaccine was 69% (95% CI = 41-83) in the high compliance category and 86% (95% CI = 76-92) and 84% (95% CI = 64-93) in the intermediate and low compliance groups, respectively. In contrast, the efficacy of DTP vaccine did not vary by compliance category using this case definition. The attack rate in children vaccinated with diphtheria and tetanus toxoids vaccine (DT) was twofold less in low compliance physician practices when compared with the rates in high and intermediate groups. The DT/DTaP and DT/DTP fold-change differences were less in the high compliance group compared with the intermediate and low compliance groups.

CONCLUSIONS

Our data suggest that observer compliance (observer bias), can significantly inflate calculated vaccine efficacy. It is likely that all recently completed efficacy trials have been effected by this type of observer bias and all vaccines have considerably less efficacy against mild disease than published data suggest.

Comparative Efficacy of the Lederle/Takeda acellular pertussis component DTP (DTaP) vaccine and Lederle whole-cell component DTP vaccine in German children after household exposure. Pertussis Vaccine Study Group

BACKGROUND

A household contact substudy was performed as part of a prospective, cohort pertussis vaccine efficacy trial in Germany.

DESIGN

Infants received four doses of either the Lederle/Takeda acellular pertussis component diphtheria-tetanus toxoids (DTP) vaccine (DTaP) or Lederle whole-cell component DTP vaccine at 3, 4.5, 6, and 15 to 18 months of age (Wyeth-Lederle Vaccines and Pediatrics, Pearl River, NY). An open control group received three doses of diphtheria and tetanus toxoids vaccine (DT) at 3, 4.5, and 15 to 18 months of age. Vaccine efficacy rates were calculated using a number of principal and ancillary case definitions for primary, secondary, and noncases by analyzing secondary attack rates in study infants after exposure to pertussis in the household using 7- to 28- and 7- to 42-day postexposure observation periods and the inclusion and the exclusion of noncases who received macrolide antibiotics or trimethoprim-sulfamethoxazole during the exposure period.

RESULTS

During a 3.5-year study period, 10271 infants (DTP or DTaP, n = 8532; DT, n = 1739) were enrolled and actively followed along with all household members for cough illnesses. Depending on the case definition, 160 to 519 household exposures to pertussis were identified. In general, secondary attack rates in DT recipients were low and this was primarily because of the frequent use of antimicrobial prophylaxis. Using the principal case definitions and the exclusion of noncases who received macrolide antibiotics or trimethoprim-sulfamethoxazole during the exposure period and the 7- to 42-day observation period, the efficacy of DTP against cough illness of greater than or equal to 7 days duration caused by Bordetella pertussis was 84% (95% confidence interval [CI] = 65-93) and that of DTaP was 58% (95% CI = 30-75). Using similar criteria, the efficacy against typical pertussis (greater than or equal to 21 days of cough with either paroxysms, whoop, or posttussive vomiting) was 94% (95% CI = 77-99) and 86% (95% CI = 62-95) for DTP and DTaP, respectively. The efficacy against any cough illness (with or without) laboratory confirmation was 54% (95% CI = 32-69) and 38% (95% CI = 13-56) for DTP and DTaP, respectively.

CONCLUSION

This household contact substudy within our cohort study, with active investigator-generated surveillance, was a severe test of vaccine efficacy. Both vaccines (DTP and DTaP) are better at preventing typical pertussis than mild illness. When case definitions similar to those in other recent trials are used, the Lederle/Takeda vaccine has an efficacy similar to other multicomponent DTaP vaccines.

Epidemiology of pertussis in French hospitals in 1993 and 1994: thirty years after a routine use of vaccination

BACKGROUND

Despite widespread vaccination during 30 years, the hypothesis of a resurgence of pertussis in France has been raised by outbreaks and sporadic case reports. No surveillance data were available after 1985.

METHODS

A survey was undertaken in 1993 and 1994 in a pediatric hospital network able to confirm cases; the network (22 hospitals) represents 19.6% of pediatric admissions in France. Case definition included clinical (> or = 21 days of paroxysmal cough), laboratory-confirmed (culture or serology by immunoblot) or epidemiologically confirmed pertussis (documented contact with a laboratory-confirmed case). The pattern of transmission was studied in the household. Vaccine status was obtained from health records.

RESULTS

during a 15-month period 560 cases (316 index cases, 244 household contact cases) were reported; 49% of index cases and 20% of contact cases were confirmed by culture and/or serology. Sixty-five percent of index cases were younger than 1 year of age (the incidence in this age group could be estimated to be 95/100000) and 66% were hospitalized for a mean duration of 2 weeks. Infection was acquired from parents (34%) and siblings (46%). Seventy-three percent of index cases were unvaccinated.

CONCLUSIONS

Although pertussis vaccination coverage is very high in France, the organism is still circulating, affecting, within the pediatric population, mostly non- or incompletely vaccinated infants. These results strongly support the importance of adhering to the immunization schedule and suggest introducing booster dose(s) to prolong vaccine immunity and reduce the exposure to Bordetella pertussis of infants too young to be immunized.

Factors influencing the spread of pertussis in households

The objective of this study was to compare the spread of pertussis in children and adults being secondary contacts after household exposure. The study was nested in an efficacy trial of an acellular pertussis vaccine. The spread of the disease was also monitored with respect to gender and antibiotic therapy. A total of 453 index cases, of which 133 were monitored for adult disease, fulfilled the WHO definition of pertussis. They had contacts to 173 unvaccinated children aged 6-47 months, and a total of 101 adults with pertussis were followed. Detection of the bacteria, or a significant increase of specific antibodies confirmed the diagnosis. Secondary spread of the disease was assumed, when a household member coughed for 7 days or more and had laboratory evidence for pertussis. Crude attack rates (AR) were 69% in children and 31% in adults (P < 0.05). AR in children were independent of gender but more women than men (P=0.02) were affected in those households where the index case was a child. Erythromycin treatment of the index case reduced the AR in exposed toddlers from 80% to 57% (P=0.06), and in exposed adults from 40% to 21% (P=0.2). Erythromycin therapy in contacts did not alter the clinical course of the disease significantly.

CONCLUSIONS

In a household study of pertussis, 69% of children and 31% of adults (more women than men) contracted the disease. Erythromycin reduced the number of infections in household contacts, but did not alter the clinical course in those who contracted pertussis.

Economic evaluation of pertussis prevention by whole-cell and acellular vaccine in Germany

Acellular pertussis vaccines are less reactogenic than whole cell pertussis vaccines, but they are also more expensive. Based on simulation models, we compared the costs and effects of three alternative pertussis vaccination strategies in German children to "no prevention": (1) vaccination with whole-cell vaccine at 45% coverage (vaccine efficacy 90%), (2) vaccination with acellular vaccine at 45% coverage (vaccine efficacy 85%), and (3) vaccination with acellular vaccine at 90% coverage. In the two low coverage scenarios expected annual savings in direct medical costs through prevention of disease were larger for whole-cell than for acellular vaccination (252 vs 216 million DM, respectively). Direct costs for treating the more important adverse events induced by whole-cell vaccination (16.9 million DM annually) did not outweigh the higher direct costs of pertussis infections not prevented with the acellular vaccine and the higher price of the acellular vaccine. However, vaccination with acellular pertussis vaccine rapidly becomes as cost saving as vaccination with whole-cell vaccine as soon as vaccination coverage can be raised from 45% to 52.5% with acellular vaccine. Acellular vaccination is also the superior alternative when considering indirect cost savings resulting from reduction in work-loss due to adverse events.

CONCLUSION

In our simulations, the most cost-effective pertussis prevention strategy was the use of an effective whole-cell vaccine with a high coverage rate. Introduction of the more expensive acellular pertussis vaccines becomes cost saving if at least a 7.5% increase in coverage is achieved. If also non-medical indirect costs to parents resulting from vaccine associated side-effects are accounted for, acellular vaccines may be more cost-effective also in countries with already high whole-cell vaccine coverage.

A comparative efficacy trial in Germany in infants who received either the Lederle/Takeda acellular pertussis component DTP (DTaP) vaccine, the Lederle whole-cell component DTP vaccine, or DT vaccine

BACKGROUND

The goal of the trial was to determine the efficacy of a multicomponent acellular pertussis vaccine against Bordetella illnesses in comparison with a whole-cell product and DT.

DESIGN

In a randomized, double-blind fashion, 2- to 4-month-old infants received 4 doses of either DTP or DTaP vaccine at 3, 4.5, 6, and 15 to 18 months of age. The controls received 3 doses (3, 4.5, 15 to 18 months of age) of DT vaccine. The DTP vaccine was Lederle adsorbed vaccine (licensed in the United States) and DTaP was Lederle/Takeda adsorbed vaccine. Follow-up for vaccine efficacy started 2 weeks after the third dose (DTP/DTaP) and at the same age (6.5 months) in DT recipients. Reactogenicity of all doses of all three vaccines was documented by standardized parent diary cards. In addition, all subjects were monitored for respiratory illnesses and serious adverse events by biweekly phone calls.

RESULTS

From May 1991 to January 1993, a total of 10 271 infants were enrolled: 8532 received either DTP or DTaP and 1739 received DT. Specific efficacy against B pertussis infections with cough >/=7 days duration was 83% (95% confidence interval [CI]: 76-88) and 72% (95% CI: 62-79) for DTP and DTaP, respectively; results for DTP and DTaP based on >/=21 days of cough with either paroxysms, whoop or posttussive vomiting (PWV) were 93% (95% CI: 89-96) and 83% (95% CI: 76-88), respectively. For DTaP vaccine, efficacy was higher after the fourth dose as compared with its efficacy after the third dose (78% vs 62% for cough >/=7 days and 85% vs 76% for cough >/=21 days with PWV). For DTP vaccine, efficacy was less varied after the third and fourth dose (78% vs 85% for cough >/=7 days and 93% vs 93% for cough >/=21 days with PWV). In contrast with DTP, the DTaP vaccine had some efficacy against B parapertussis infection (point estimate for cough >/=7 days: 31% [95% CI: -10-56]). All vaccines were generally well-tolerated. However, side reactions were significantly less after DTaP compared with DTP.

CONCLUSIONS

Like other multicomponent acellular pertussis vaccines, the Lederle/Takeda DTaP vaccine demonstrated good efficacy against mild and typical pertussis due to B pertussis infections. Interestingly, it also may have some efficacy against B parapertussis. Based on the results of this trial, the vaccine was licensed in the United States in December 1996 for all 5 doses of the currently recommended immunization schedule in this country.

Clinical findings in Bordetella pertussis infections: results of a prospective multicenter surveillance study

OBJECTIVE

To study the clinical presentation of culture-confirmed pertussis in children and their contacts with cough illnesses in an outpatient setting.

METHODOLOGY

In conjunction with a large pertussis vaccine efficacy trial in Germany, a central laboratory to isolate Bordetella species from nasopharyngeal specimens was established in Erlangen in October 1990. Pediatricians in private practices in southern Germany, the Saar region, and Berlin were encouraged to obtain nasopharyngeal specimens and clinical characteristics from patients with cough illnesses >/=7 days' duration. Bordetella species were isolated by use of calcium alginate swabs, Regan-Lowe agar, and modified Stainer-Scholte broth. Clinical characteristics were determined by initial and follow-up questionnaires.

RESULTS

From October 1990 to September 1996, 20 972 specimens were submitted, and B pertussis was isolated in 2592 instances (12.4%). Of the culture-proven cases, 50.7% were female, and the age range was 6 days to 41 years, with a mean and median of 4.3 years and 4.1 years, respectively. The following characteristics were noted. Only 4% of the patients had received pertussis vaccine. Of unvaccinated patients, 90.2% had paroxysmal cough, 78.9% demonstrated whooping, and 53.3% presented with posttussive vomiting; 5.7% had fever >/=38 degrees C. The duration of cough was </=4 weeks in 37.9% and </=3 weeks in 17.4%. Leukocytosis and lymphocytosis (values above the age-specific mean) were observed in 71.9% and 75.9% of unvaccinated patients, respectively. The overall complication rate was 5.8%, and pneumonia (29%) was the most frequent complication. In infants <6 months of age, the rate of complications was 23.8%. One death in a 7-month-old infant occurred.

CONCLUSIONS

Typical symptoms of pertussis were observed in the great majority of patients regardless of age group. However, the duration of cough was surprisingly short in one sixth of the patients. These short illness cases would not be classified as pertussis according to the World Health Organization clinical case definition, which requires >/=21 days of spasmodic cough.

Polymerase chain reaction (PCR) compared with conventional identification in culture for detection of Bordetella pertussis in 7153 children

OBJECTIVE: To compare the polymerase chain reaction (PCR) results with conventional culture results for the diagnosis of Bordetella pertussis infections. METHODS: PCR and culture were performed in the course of a large vaccine efficacy trial in Germany on specimens taken from 7153 children less-than-or-equal2 years of age with cough illness lasting >6 days, and laboratory results were compared with clinical data also obtained from the patients. Calcium alginate nasopharyngeal swabs were taken for culture and clinical data were obtained from patients. Swabs were inoculated on charcoal horse blood agar plates containing cephalexin, and then discarded. The agar plates were preincubated for 2 days at the physician's office and then shipped to the culture laboratory at the University Children's Hospital in Munich, Germany, for diagnosis of B. pertussis and B. parapertussis infections. In this laboratory, Dacron swabs for PCR were taken from each culture by a wide sweep over the culture. Swabs for PCR were stored in NaCl and sent weekly to the PCR laboratory at the University Children's Hospital in Basel, Switzerland, for PCR diagnosis of B. pertussis infections. RESULTS: B. pertussis was identified by culture in 3% (213/7153) and by PCR in 7.6% (546/7153) of the specimens. Therefore, PCR increased the identification rate of subjects with B. pertussis infection 2.6-fold. Clinical characteristics were considered according to the type of laboratory findings: group 1 consisted of 209 culture-positive and PCR-positive subjects, and group 2 of 337 culture-negative but PCR-positive subjects. Group 2 subjects were significantly more likely to have mild or atypical clinical symptoms of whooping cough than were group 1 subjects. By analyzing the PCR results of group 2 subjects semiquantitatively, it could be shown that the degree of PCR positivity correlated with the severity of the clinical symptoms of whooping cough in the patient. CONCLUSIONS: PCR identified many pertussis cases with mild or atypical clinical symptoms that were not identified by culture. Semiquantification of PCR products revealed that the less positive the PCR result, the higher was the failure rate in diagnosing pertussis by culture, and, in addition, the less typical were the clinical symptoms in the patient.

Comparative efficacy of acellular pertussis vaccines: an analysis of recent trials

Diphtheria-tetanus-acellular pertussis vaccines have been licensed in the United States since 1991. Compared with the whole cell pertussis component diphtheria-tetanus-pertussis vaccine, the diphtheria-tetanus-acellular pertussis vaccines were found in reactogenicity and immunogenicity studies to be immunogenic with respect to their specific antigen content and to be associated with less severe and less frequent adverse reactions. A case definition of pertussis was developed by the World Health Organization for use in vaccine efficacy trials, but this definition eliminates some laboratory-confirmed cases from efficacy calculations. Because these cases are more common in vaccinees than in controls, vaccine efficacy appears better than it truly is whereas less effective vaccines seem comparable with their more effective counterparts. In addition observer bias may contribute to the appearance of enhanced efficacy of the less effective vaccines, which tend to prevent typical but not mild disease. When analyzing efficacy based on prevention of laboratory-confirmed pertussis with cough > or = 7 days, single component pertussis toxin (PT) toxoid vaccines were found to be less effective than two-component PT toxoid/filamentous hemagglutinin vaccines, and three- or four-component vaccines containing pertactin in addition to PT toxoid and filamentous hemagglutinin were more effective than either the single-component or two-component vaccines.

Bordetella pertussis infections and sudden unexpected deaths in children

From December 1990 to November 1993 nasopharyngeal specimens were obtained for culture from 50 children (mean 4.9 +/- 3.3 months of age) who had died suddenly. Bordetella pertussis was not isolated. Subsequently, nasopharyngeal specimens for polymerase chain reaction (PCR) analysis were obtained from another 51 victims of sudden death (mean 5.4 +/- 4.4 months of age); nine (18%) were B. pertussis positive.

CONCLUSION

Our findings support previous epidemiological studies which noted an association between epidemic pertussis and sudden infant death syndrome. Further PCR studies with both internal and external controls should be performed.

Whooping-cough vaccination: historical, social and political controversies

New acellular whooping cough vaccines may have the effect of leading us to forget that infectious diseases such as whooping cough have declined in the context of particular historical, social conditions and persist in the context of particular types of social inequalities. The debates over the existence of damage from whole-cell whooping cough vaccine, and the respective risks of the vaccine and the disease are still unresolved owing to methodological limitations of studies on both sides of the argument. One-sided health 'education' campaigns on whooping cough vaccine have questionable ethics, and suppression of dissenting views is counterproductive. Health professionals and parents have a right to know the political context of the debate.