Pertussis complications in Germany--3 years of hospital-based surveillance during the introduction of acellular vaccines

Bordetella pertussis in School-Age Children, Adolescents and Adults: A Systematic Review of Epidemiology and Mortality in Europe

Pertussis (whooping cough) epidemics persist globally despite high vaccine coverage among infants and young children. The resurgence of pertussis in high-income countries is partly due to waning vaccine immunity, resulting in a pool of unprotected adolescents and adults. However, pertussis is generally less severe in adolescents and adults, and this difference in presentation means it can often be unrecognised by healthcare professionals, meaning that it is largely under-diagnosed in older populations. A systematic search of MEDLINE, EMBASE and BIOSIS was undertaken to identify studies published between 1 January 1990 and 17 June 2019, with information on pertussis epidemiology and mortality in school-aged children, adolescents and adults in Europe. A formal statistical comparison (e.g. using meta-analyses) was not possible because of the mix of methodologies reported. There were 69 epidemiological studies and 19 mortality studies identified for review. Over the past decade, the reported incidence of notified pertussis cases varied widely between European countries, which is likely associated with differences in surveillance systems, diagnostic techniques and reporting regulations. However, several studies show that pertussis is circulating among adolescents and adults in Europe, and although pertussis-related morbidity and mortality are highest in infants, there is evidence that adults aged > 50 years are at increased risk. For example, in a hospital-based surveillance study in Portugal, between 2000 and 2015, 94% of hospitalised pertussis cases were infants aged < 1 year, with a case fatality rate (CFR) of 0.8%; however, among hospitalised adult cases of pertussis, the CFRs were 11.5% (aged 18–64 years) and 17.4% (aged > 65 years). Very few European countries currently include pertussis boosters for adults in the national immunisation strategy. In addition to increasing pertussis vaccination coverage in adolescents and adults, mitigation strategies in European countries should include improved diagnosis and treatment in these populations.

Pertussis hospitalizations among term and preterm infants: clinical course and vaccine effectiveness

BACKGROUND

Pertussis causes severe disease in young unvaccinated infants, with preterms potentially at highest risk. We studied pertussis in hospitalized infants as related to gestational age (GA) and vaccination history.

METHODS

Medical record data of 0-2y old patients hospitalized for pertussis during 2005-2014 were linked to vaccination data. Multivariable logistic regression was used to study the association between GA and vaccination history on the clinical disease course. We compared vaccine effectiveness (VE) against hospitalization for pertussis between term and preterm infants (i.e., <37w GA) using the screening method as developed by Farrington.

RESULTS

Of 1187 records, medical data from 676 were retrieved. Of these, 12% concerned preterms, whereas they are 8% of Dutch birth cohorts. Median age at admission was 3 m for preterms and 2 m for terms (p < 0.001). Preterms more often had received pertussis vaccination (62% vs 44%; p = 0.01) and more often had coinfections (37% vs 21%; p = 0.01). Preterms tended more often to have complications, to require artificial respiration or to need admittance to the intensive care unit (ICU). Preterms had longer ICU stays (15d vs 9d; p = 0.004). Vaccinated preterms and terms had a lower median length of hospital stay and lower crude risks of apneas and the need for artificial respiration, additional oxygen, and ICU admittance than those not vaccinated. After adjustment for presence of coinfections and age at admittance, these differences were not significant, except the lower need of oxygen treatment in vaccinated terms. Effectiveness of the first vaccination against pertussis hospitalizations was 95% (95% CI 93-96%) and 73% (95% CI 20-91%) in terms and preterms, respectively. Effectiveness of the second dose of the primary vaccination series was comparable in both groups (86 and 99%, respectively).

CONCLUSIONS

Infants hospitalized for pertussis suffer from severe disease. Preterms were overrepresented, with higher need for intensive treatment and less VE of first vaccination. These findings stress the need for alternative prevention, in particular prenatal vaccination of mothers, to reduce pertussis in both groups.

Surveillance of pertussis: methods and implementation

INTRODUCTION

Pertussis or whooping cough is a respiratory disease caused by Bordetella pertussis or, to a lesser extent, by B. parapertussis. Vaccines against pertussis have been widely used for more than 50 years and have led to a significant reduction of morbidity and mortality. However, even in countries with a high vaccine coverage, the disease is still not well controlled. Surveillance is urgently needed.

AREAS COVERED

This review summarizes surveillance methods and gives examples that may be used when setting up a surveillance program or analyzing an outbreak. Expert commentary: Pertussis surveillance is urgently required in order to define the burden of disease, to adapt vaccine strategies according to the type of pertussis vaccine used and to follow the evolution of the bacteria.

Pertussis: not only a disease of childhood

INTRODUCTION

Pertussis is not just a childhood disease, but a respiratory infection that causes persistent cough in all age groups, from newborns to the elderly.

METHODS

The authors performed a selective literature search and reviewed national and international recommendations for treatment and vaccination.

RESULTS

Pertussis is found principally in young unvaccinated infants, but school-age children, adolescents, and adults are also affected. Up to 1% of infants contract pertussis, and their respiratory symptoms are often accompanied by apnea. School-age children occasionally display the coughing spasms typical of the disease. Annually, 0.2% to 0.5% of all adolescents and adults are infected and suffer from prolonged, frequently non-paroxysmal coughing. Severe and fatal cases of pertussis occur mainly in newborns and infants, and 25% of affected adults experience complications. Bordetella DNA may be detected by polymerase chain reaction (PCR) for four weeks after symptom onset; except in infants, the sensitivity of this diagnostic technique is low. Although the diagnosis can be confirmed by serological tests, the methods are not well standardized. Treatment with a macrolide prevents the spread of infection, but generally does not alleviate the symptoms. Combination vaccines are the most effective means of prophylaxis.

DISCUSSION

Pertussis is usually not included in the differential diagnosis of persistent respiratory symptoms. The considerable burden of disease could be reduced in adults and young infants by vaccinating adults with acellular combination vaccines.

Prevention of pertussis: Recommendations derived from the second Global Pertussis Initiative roundtable meeting

The Global Pertussis Initiative (GPI) was established in 2001 to assess the global extent of the ongoing problem of pertussis and to evaluate and prioritize pertussis control strategies. Exchange of data, knowledge, and experience, facilitated by discussion and debate, resulted in the formulation, in 2002, of the following recommendation: all countries should consider expanding existing vaccination strategies to include adding pertussis booster doses to pre-school children (4-6 years old), to adolescents, and to those specific adults that have the highest risk of transmitting Bordetella pertussis infection to vulnerable infants. The GPI met again in 2005, where it reinforced its previous recommendation for universal adolescent immunization. Additionally, the GPI recommended implementation of the cocoon strategy (immunization of family members and close contacts of the newborn) in countries where it is economically feasible, and encouraged efforts toward global standardization of pertussis disease clinical definitions and diagnostics. Universal adult vaccination is a logical goal for the ultimate elimination of pertussis disease, but feasibility issues remain obstacles to implementation.

Comparison of acellular pertussis vaccines-induced immunity against infection due to Bordetella pertussis variant isolates in a mouse model

A significant increase in the incidence of pertussis in adolescents and adults has been observed in vaccinated populations. Concomitantly, emergence of novel pertussis toxin and pertactin types in circulating Bordetella pertussis isolates was noticed. In this study, immunity induced by acellular vaccines against infection due to isolates expressing different pertactin types and fimbriae was monitored in a mouse model. In accordance with previous studies, the effect of a bicomponent DTPa vaccine on bacterial clearance was lower when compared with tri- or pentavalent DTPa vaccines. Whatever the isolates used to infect mice, the tri- or pentavalent DTPa vaccines were both efficacious in inducing immunity that resulted in clearance of infection. These findings suggest that re-emergence of pertussis might not be related to emergence of isolates escaping vaccine protection. The present study reduces potential concerns about acellular vaccine efficacy, but frequent monitoring of protection and surveillance of the evolution of the B. pertussis population remains of particular importance.

Health burden of pertussis in infants and children

In countries with high rates of vaccination against pertussis, the incidence of this disease has decreased dramatically compared with the prevaccine era. However, pertussis still occurs in these countries, and severe morbidity and mortality are greatest among infants, particularly those who are unimmunized or incompletely immunized. Pertussis in older children and adults is perceived by many as being a mild disease, but it is a significant health burden in persons of all ages. Infants with pertussis experience the highest rates of hospitalization, complications and death. Severe complications include pneumonia, encephalopathy and meningoencephalitis. In addition, infants may experience weight loss, bronchitis, otitis media, apnea, cyanosis, inguinal hernia and rectal prolapse. It is essential to explore methods to prevent disease transmission to infants in the months before they complete their primary immunization series. The Global Pertussis Initiative was established to assess the true health burden of pertussis in infants and to suggest strategies to combat transmission and infection with Bordetella pertussis, which remains a significant public health concern.

Diagnosis and management of pertussis

Pertussis is increasing in frequency among children too young to be vaccinated and among adolescents and adults. This increase is due mainly to waning immunity among vaccinated individuals, who become susceptible during adolescence and adulthood and maintain the circulation of Bordetella pertussis. Infants are at highest risk of severe illness requiring hospital admission, complications and death. The clinical presentation in adolescents, adults and vaccinated individuals may be atypical, with paroxysmal cough of short duration or simply a persistent cough. Culture and polymerase chain reaction may be used to identify B. pertussis infection, but their sensitivity is high only in the early phase of the disease. Serologic tests are not standardized for the diagnosis of pertussis, and their clinical application is limited. Erythromycin is still considered in some countries to be the "gold standard" for therapy and prophylaxis; however, azithromycin and clarithromycin seem equally efficacious and are associated with fewer side effects.

National study of infants hospitalized with pertussis in the acellular vaccine era

BACKGROUND

In Australia in 1999 acellular pertussis vaccine (DTPa) replaced locally manufactured whole cell vaccine given at 2, 4 and 6 months of age with coverage of about 95% by 12 months of age. Few data are available on pertussis hospitalizations or sources of infection in countries exclusively using DTPa.

METHODS

In 2001 national active monthly surveillance of infant hospitalizations for pertussis was conducted through the Australian Pediatric Surveillance Unit, which surveys all child health specialists monthly. A standard questionnaire was completed for notified cases.

RESULTS

There were 140 infants reported (median age at diagnosis, 8 weeks). The rate of hospitalization in indigenous infants was significantly higher than in nonindigenous infants (P < 0.01). Of 97 (69%) infants who had not been vaccinated for pertussis, 63 (65%) were <8 weeks old (before the first scheduled dose of DTPa vaccine). Of 76 infants age > or =8 weeks, only 28 (37%) were appropriately immunized for age. Of 68 coughing contacts whose ages were known, 46 (68%) were adults, usually one of the infant's parents. Of 32 child contacts 16 (50%) were siblings. Four infants <6 weeks old died.

CONCLUSION

Despite universal vaccination with DTPa in Australia, pertussis remains an important cause of hospitalization, morbidity and death in infants, most of whom were too young to be vaccinated or had missed vaccinations. The most common source of infection was a parent. Strategies to improve pertussis control in countries with high DTPa coverage could include adult-formulated booster pertussis vaccines for adolescents and recent parents and/or accelerated pertussis vaccine schedules for infants.

Diagnostic testing and discharge coding for whooping cough in a children's hospital

OBJECTIVE

To evaluate the diagnostic pathways for whooping cough in a large urban paediatric hospital to inform assessment of the relative merits of notification and hospitalization data for measuring pertussis disease burden in Australian children.

METHODS

All laboratory requests for Bordetella pertussis (BP) culture or serology between 30 June 1997 and 30 June 1999 were reviewed and cross-checked against discharge diagnoses with International Classification of Disease (ICD) codes A37.0, 033.0 (whooping cough due to BP) or 37.9, 033.9 (whooping cough due to unspecified organisms). Culture-positive (CP) cases were defined as a positive culture or polymerase chain reaction for BP. Culture-negative (CN) cases either fulfilled the current Australian clinical case definition (>/=14 days of cough with one or more of paroxysms, whoop, post-tussive vomiting), or had a cough illness with either positive BP serology or documented contact with an individual coughing for >14 days. In infants <6-months-old, a coughing illness with apnoea and negative investigations for other causes was also accepted. Culture positive and CN cases were cross-referenced with notification data.

RESULTS

During the study period, laboratory tests for BP were performed in 677 children, of whom 230 were hospitalized and 71 (31%) had an eligible ICD code at discharge; 29 were CP, 40 CN, and two (3%) were misclassified. A further 14 CP children were not admitted. Although 61 hospitalized cases (88%) fulfilled notification criteria, including 32 (80%) of CN cases, only 26 (90%) of CP and eight (20%) of CN cases were notified.

CONCLUSIONS

Notifications substantially under-enumerate hospitalized infant cases, especially those without positive laboratory tests. Hospital discharge data add significantly to surveillance for pertussis, particularly in infancy where most severe cases occur.

Effectiveness of acellular pertussis vaccine assessed by hospital-based active surveillance in Germany

We assessed the effectiveness of complete and partial pertussis vaccination in Germany--a country where acellular vaccine is predominantly used--for the prevention of cases of pertussis requiring hospitalization. Vaccine effectiveness was estimated by means of a screening method. Vaccine coverage of children born during the period of June 1996 through December 1998 was assessed by a telephone survey. Data from hospitalized children with pertussis in 1997-1998 and from patients with pertussis complications in 1997-2000 were acquired by a nationwide, hospital-based, active surveillance system. Age-adjusted vaccine effectiveness of completed primary vaccination was estimated to be 99.8% (95% confidence interval [95% CI], 98.9-100). After receipt of 1 dose of vaccine, vaccine effectiveness was as high as 68.0% (95% CI, 45.6-81.1), increasing to 91.8% (95% CI, 84.7-95.7) after receipt of the second dose. Vaccine effectiveness was even slightly higher for pertussis with complications. Thus, even after partial vaccination, acellular pertussis vaccine is highly effective in preventing hospitalizations for pertussis.