Pertussis: an old disease that is still with us

Prospective pertussis surveillance in Switzerland, 1991-2006

Pertussis has been monitored in Switzerland since 1991 by the nationwide Swiss Sentinel Surveillance Network (SSSN), consisting of approximately 200 general practitioners, internists and pediatricians representing about 3% of the total primary care physicians of these specialities. SSSN members report patients with cough ≥ 14 days plus either an epidemiological link or characteristic symptoms (paroxysms, whoop, post-tussive vomiting) on a weekly basis to the Federal Office of Public Health. Confirmatory PCR from nasopharyngeal specimens is offered for free. A total of 4992 cases have been reported until 2006. Yearly incidence has dropped from 70 cases per 100,000 inhabitants in 1992 to 40 in 2006, with a single epidemic in 1994-1995 with 280-370 cases/100,000. On average 80% of reported cases were tested by PCR, 24% of these were confirmed as Bordetella pertussis infections. For 2.6% of patients complications were reported, most commonly pneumonia, asthma bronchiale, otitis media, bronchitis and rib fractures. On average, 1.5% of patients were hospitalized. Disease in vaccinated patients was mitigated with less frequent complications (unvaccinated: 5.1%; 3 doses: 3.0%; ≥ 4 doses: 1.7%), hospitalizations (unvaccinated: 3.6%; ≥ 1 dose: 1.1%) and various clinical symptoms compared to unvaccinated patients. Comparing the periods 1991-1996, 1997-2001 and 2002-2006, a shift of pertussis from age group 1-9 years to 10-19 and ≥ 40 years was observed among patients cared for by general practitioners and internists. The benefits of further booster doses in adolescents and/or adults need to be considered.

Dose response of attenuated Bordetella pertussis BPZE1-induced protection in mice

Despite the availability of efficacious vaccines, the incidence of whooping cough is still high in many countries and is even increasing in countries with high vaccine coverage. Most severe and life-threatening pertussis cases occur in infants who are too young to be sufficiently protected by current vaccine regimens. As a potential solution to this problem, we have developed an attenuated live Bordetella pertussis vaccine strain, named BPZE1. Here, we show that after a single administration, BPZE1 induces dose-dependent protection against challenge with virulent B. pertussis in low-dose and in high-dose intranasal mouse lung colonization models. In addition, we observed BPZE1 dose-dependent antibody titers to B. pertussis antigens, as well as cell-mediated immunity, evidenced by the amounts of gamma interferon (IFN-gamma) released from spleen cells upon stimulation with B. pertussis antigens. These two parameters may perhaps be used as readouts in clinical trials in humans that are currently being planned.

Seroprevalence of pertussis antitoxin (anti-PT) in Sweden before and 10 years after the introduction of a universal childhood pertussis vaccination program

The prevalence of IgG ELISA antibodies against pertussis toxin (anti-PT) was studied in two Swedish seroepidemiological studies. One was performed in 1997 when the new pertussis vaccination program was 1 year old (n = 3420). In 2007, when Pa vaccines had been used countrywide for 10 years in the universal child vaccination program, this study was repeated to analyze the effect of vaccination on anti-PT prevalence (n = 2379). Before the statistical analysis of seroprevalence, children vaccinated within the last 2 years before the serosurveys were excluded. The results indicate a reduced exposure to Bordetella pertussis in the population. The proportion of sera without measurable anti-PT antibodies increased significantly, aggregated over all comparable age groups, from 3.8% in people sampled in 1997 to 16.3% in people sampled in 2007. For cord blood, 1% was without measurable anti-PT antibodies in 1997 compared to a significantly higher level, 12%, in 2007. With anti-PT concentrations of ≥50 and ≥100 EU/ml as cutoff points for ‘recent infection’ the proportion above the cutoff points for younger children was significantly higher in 1997 than in 2007 at both cutoff points. For all adults, 20 years of age and older, the difference in proportions above the lower cutoff point was close to statistically significant, comparing 1997 with 2007. This was not the case at 100 EU/ml. In the 1997 samples of children, there was a significant downward trend of ‘recent infections’ at both cutoff points for three sampled age groups between 5 and 15 years of age from 21% at 5.0–5.5 years of age to 7% at 14.7–15.7 years for the lowest cutoff. In the 2007 samples of children, on the contrary, there was a significant continuous upward trend of ‘recent infections’, at both cutoff points, for four sampled age groups between 4 and 18 years of age – from 4% at 4–5 years of age to 16% at 17–18 years at the lowest cutoff. The continuous increase, with age of children with high anti-PT concentrations, supports the recent change in the general Swedish childhood vaccination program to include a pre-school booster at 5–6 years and a school-leaving booster at 14–16 years of age.

Maternally derived antibodies against Bordetella pertussis antigens pertussis toxin and filamentous hemagglutinin in preterm and full term newborns

We measured IgG-anti-pertussis toxin and -IgG-anti-filamentous hemagglutinin antibody values in 43 full term and 34 preterm infants and 79 mothers. Antibody values were generally low and mean values were higher in full term than preterm infants. Transfer ratios increased with gestational age of the newborns. Based on these findings, maternal and neonatal immunization strategies should be considered to protect young infants from pertussis.

Perfil epidemiológico da coqueluche no Rio Grande do Sul, Brasil: estudo da correlação entre incidência e cobertura vacinal

No Estado do Rio Grande do Sul, Brasil, foi constatado que a coqueluche apresentou uma tendência crescente desde o ano 2000, levando à deflagração de alerta epidêmico em 2004, conforme boletins epidemiológicos emitidos pelos órgãos governamentais de saúde. Nosso objetivo neste estudo foi identificar o perfil epidemiológico da coqueluche nesse estado; para tanto, utilizamos a incidência da notificação da doença entre janeiro de 1995 e dezembro de 2004, a porcentagem de cobertura vacinal e a caracterização da população afetada. Construiu-se um diagrama de controle para determinar a magnitude da doença em 2004; para a análise da correlação entre incidência e cobertura vacinal foi estabelecida a oscilação entre as curvas de cobertura vacinal e de notificação de casos nos últimos dez anos. No Rio Grande do Sul, a coqueluche esteve em nível epidêmico em 2004, representando importante causa de morbimortalidade em crianças menores de um ano, apesar da disponibilidade de vacinas eficazes e de altas taxas de cobertura vacinal informadas nos últimos anos. Portanto, serão necessários estudos sobre o comportamento da doença nos próximos anos e determinação de possíveis fatores envolvidos nesse ressurgimento.

Detection of anti-pertussis toxin IgG in oral fluids for use in diagnosis and surveillance of Bordetella pertussis infection in children and young adults

Bordetella pertussis infection is being increasingly recognized as a cause of prolonged, distressing cough (without whooping symptoms) in children and young adults. Diagnosis of infection in this population is important for treatment and surveillance purposes, and may also prove useful in reducing transmission to unvaccinated babies, for whom disease can be fatal. Serum IgG titres against pertussis toxin (PT) are routinely used as a marker of recent or persisting B. pertussis infection. However, collection of serum from young children is difficult, and compliance amongst these subjects to give samples is low. To circumvent these problems, an IgG-capture ELISA capable of detecting anti-PT IgG in oral fluid was devised. The assay was evaluated by comparison to a serum ELISA, using 187 matched serum and oral fluid samples from children (aged 5–16 years) with a history of prolonged coughing, whose serum anti-PT titre had already been determined (69 seropositive, 118 seronegative). The results showed that, using a cutoff of 70 arbitrary units (AU), the oral fluid assay detected seropositive subjects with a sensitivity of 79.7 % [95 % confidence interval (CI) 68.3–88.4] and a specificity of 96.6 % (95 % CI 91.5–99.1). Thus, oral fluid titres of ⩾70 AU would possess a positive predictive value of 76.2–93.2 % for pertussis amongst children with chronic coughs when used as a surrogate for the serum ELISA (assuming disease prevalence of 12–37 %). This oral fluid ELISA will greatly assist in the convenience of B. pertussis disease diagnosis and surveillance.

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.

Pertussis vaccination for adolescents and adults

Following the introduction of vaccines, the incidence of pertussis declined; however, since 1990, a progressive increase was noted, even in highly immunised populations. Periodic pertussis outbreaks are due to suboptimal efficacy of the vaccine and waning immunity with increasing age. A significant proportion of adolescents and adults with a prolonged cough present Bordetella pertussis, and infection is often transmitted to infants too young to be vaccinated. A high vaccination coverage in the whole population would be necessary to interrupt the circulation of B. pertussis, but immunisation programmes for adolescents and adults have been introduced recently and are accepted with difficulty. The lack of cost-benefit analysis and consistent epidemiological data makes it difficult to assess the role of pertussis elimination among public health priorities. At present, programmes targeted at risk groups for close contacts with infants are the most convenient for adult population, as more epidemiological and economic evidence is needed before a universal strategy can be discussed.

Low levels of antipertussis antibodies plus lack of history of pertussis correlate with susceptibility after household exposure to Bordetella pertussis

Prospectively collected data in a Swedish vaccine efficacy trial were used to investigate transmission of pertussis from small study infants to other household members. Forty one percent (258/627) of the exposed persons with paired serology had laboratory confirmed pertussis. The majority of those with laboratory confirmed pertussis had less than 14 days of cough and many were asymptomatic. High susceptibility to symptomatic pertussis was found among persons with low initial IgG antibody concentrations against pertussis toxin, especially those without previous history of pertussis vaccination or disease.

Severe and unrecognised: pertussis in UK infants

AIMS

To diagnose pertussis using culture, polymerase chain reaction, and serology, in children admitted to intensive care units (PICUs) and some paediatric wards in London, and in their household contacts to determine the source of infection.

METHODS

Infants <5 months old admitted to London PICUs between 1998 and 2000 with respiratory failure, apnoea and/or bradycardia, or acute life threatening episodes (ALTE), and children <15 years admitted to paediatric wards at St Mary's and St George's Hospitals between 1999 and 2000 with lower respiratory tract infection, apnoea, or ALTE were studied.

RESULTS

Sixty seven per cent of eligible children (142/212) were recruited; 23% (33/142) had pertussis, 19.8% (25/126) on the PICU and 50% (8/16) on wards. Two died. Only 4% (6/142) were culture positive. Pertussis was clinically suspected on admission in 28% of infants (7/25) on the PICU and 75% (6/8) on the wards. Infants on PICU with pertussis coughed for longer, had apnoeas and whooped more often, and a higher lymphocyte count than infants without pertussis. Pertussis and respiratory syncytial virus (RSV) co-infection was frequent (11/33, 33%). Pertussis was confirmed in 22/33 (67%) of those who were first to become ill in the family. For 14/33 children the source of infection was a parent; for 9/33 the source of pertussis was an older fully vaccinated child in the household.

CONCLUSIONS

Severe pertussis is under diagnosed. An RSV diagnosis does not exclude pertussis. Future changes to the UK vaccination programme should aim to reduce pertussis transmission to young infants by their parents and older siblings.