Israel Medical Association Journal

Background: An outbreak of pertussis occurred in a daycare center with 87.5% vaccination coverage.

Objectives: To assess the effectiveness of the acellular pertussis vaccine and prevention of pertussis after chemoprophylaxis with azithromycin.

Methods: We studied 31 daycare children aged 3–5.5 years exposed to a child with pertussis. Nasopharyngeal swabs were obtained for Bordetella pertussis culture and polymerase chain reaction initially, and at days 21 and 60 of follow-up, in cases exhibiting symptoms.

Results: Of the 31 daycare children 6 (19%) tested positive for B. pertussis by PCR[1], 4 of whom had not been vaccinated against the disease. Of the two vaccinated children who contracted pertussis, one had milder symptoms and the other was asymptomatic. The incidence of pertussis was significantly lower in the vaccinated group (2/27) than in the unvaccinated group (4/4) (P = 0.000), with efficacy of the vaccine calculated to be 92.5%. Azithromycin chemoprophylaxis was taken only by 14 of the 25 exposed children (56%). On day 21 follow-up, there was no further laboratory-diagnosed B. pertussis cases in any of the exposed children, regardless of whether or not chemoprophylaxis was taken.

Conclusions: Based on the children’s clinical manifestations and PCR findings a pertussis outbreak had occurred in the daycare center studied. Our findings support the importance of pertussis vaccination since all the unvaccinated children in the daycare center contracted the infection.

The Israel Ministry of Health’s epidemiology department reported a record number of 1564 new pertussis cases in 2004. This brings the incidence rate to 23 per 100,000 population, indicating a marked increase in the prevalence of pertussis, from 1–3/100,000 in 1998, 9 in 2001, to 14 in 2003. The rate of atypical pertussis presentations in vaccinated patients, the decline in pertussis immunity post-vaccination, and the decreased awareness of potential infections in the adult population make the diagnosis of pertussis difficult and contribute to the rising incidence. In this article we review the current literature in order to increase awareness of the occurrence of pertussis in children as well as adults, discuss the laboratory diagnostic methods being used, and report the currently recommended means of treating the disease.

Background: Pertussis is the only vaccine-preventable disease that has re-emerged in Israel. The reported crude incidence of the disease increased 16-fold since 1998.

Objectives: To describe the epidemiology of pertussis and to explain the substantial increase in reported pertussis incidence in Israel in recent years.

Methods: Crude and specific pertussis incidence by age, patient immunization status, hospitalization rate and national immunization coverage rate were calculated from information provided by the public health offices of the Ministry of Health.

Results: The reported crude incidence of pertussis increased from 1–2/100,000 in 1994–98 to 23/100,000 in 2004. The trend was observed in all age groups, being most prominent in infants under age 1 year and in children aged 5–14. The incidence of pertussis was substantially higher in unvaccinated and partly vaccinated compared to fully vaccinated persons. Fifteen percent of notified cases were hospitalized, but in infants under age 1 year the hospitalization rate was 50%. National pertussis immunization coverage by age 2 years was stable during the last 10 years.

Conclusions: There are several possible explanations for the re-emergence of pertussis in Israel. The most plausible reason seems to be the waning of vaccine-induced immunity in face of infrequent natural exposure to the infectious agent and lack of a pertussis vaccine booster dose after age 1.
 

For children born after 1 January 2005, use of the Sabin oral polio vaccine in combination with the enhanced-potency Salk inactivated polio vaccine as part of the routine vaccination schedule was discontinued. The schedule now includes only IPV [1]. In September 2005, a fifth dose of pertussis vaccine was added for pupils in their second year of elementary school. This article describes the reasons for these changes, which have rendered Israel's routine vaccination program one of the most effective in the world.

Objectives: To assess the relative efficacy of clinical and laboratory methods in the diagnosis of Bordetella pertussis by patient age and immunization status.

Methods: We compared the clinical and laboratory diagnosis of B. pertussis in 87 pre-vaccinated, 78 recently vaccinated, and 75 post-vaccinated children with suspected pertussis. Serum and nasopharyngeal swabs were obtained for serology, culture and polymerase chain reaction.

Results: PCR[1] and culture identified 41% and 7% of patients with B. pertussis, respectively (P < 0.001). All positive cultures were PCR-positive. Positive PCR was less common among those recently vaccinated than among those in the pre- (P < 0.001) and post-vaccinated groups (P < 0.05). Positive culture was more common among those pre-vaccinated than among those recently vaccinated (P < 0.01). Positive tests for immunoglobulin M and A were more common among the post-vaccinated than the pre- and recently vaccinated (P < 0.001), respectively. Logistic regression analyses revealed that clinical criteria have no significant association with infection in recently and post-vaccinated children. Among the pre-vaccinated children, whoop and cough duration were associated with a positive PCR (odds ratio 7.66 and 0.5, P < 0.001). Seventy-six percent of pre-vaccinated, 39% of recently vaccinated and 40% of post-vaccinated children with positive PCR did not meet the U.S. Centers for Disease Control diagnostic criteria for B. pertussis.

Conclusions: PCR is a useful tool for pertussis diagnosis, particularly in pre-vaccinated infants. The yield of culture and serology is limited, especially among pre- and recently vaccinated children. In pre-vaccinated infants with whoop and less than 2 weeks of cough, PCR testing should be implemented promptly.

Background: There is an increasing number of reports of pertussis among older children and adults. The development and licensure of an acellular pertussis vaccine offer the possibility of adult vaccination against the disease. Information on immunity to pertussis in this age group is needed before any vaccination policy can be considered.

Objectives: To study the seroepidemiology of pertussis antibodies in a random sample of adolescents.

Methods: Serum IgG antibodies to whole-cell lysate of Bordetella pertussis were measured by enzyme-linked immunosorbent assay in sera of 533 Israeli military recruits aged 17–18 years. Epidemiologic variables were collected by a questionnaire and analyzed for correlation with pertussis antibodies.  

Results: Of the sera tested 58.6% were positive for pertussis IgG antibodies, while 35.4% were negative and 6% were borderline. The seropositivity rate was significantly higher among females and non-smokers than among males and smokers. Serum samples of subjects found negative to Bordetella pertussis on recruitment were tested again, using the same ELISA assay, 2–3 years later.  Seroconversion during the 3 year military service was detected in 12.5% of 40 subjects. Using the pertussis toxin as the antigen in a subsample of 160 sera, the seroprevalence was lower than that detected by the whole-cell lysate on the same sera (45% vs. 58%).

Conclusions: A significant part of the adolescent population in Israel has low titer of serum IgG antibodies to the multiple antigens of B. pertussis. The relatively low concentration of anti-pertussis antibodies, together with the serological evidence of exposure to the disease indicates that booster immunization with the acellular pertussis vaccine of military recruits should be considered after more information on the incidence of clinical cases of pertussis will be available.

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ELISA = enzyme-linked immunosorbent assay