From
Emerging Infectious Diseases

Pertussis Infection in Fully Vaccinated Children in Day-Care Centers, Israel

Isaac Srugo, Daniel Benilevi, Ralph Madeb, Department of Clinical Microbiology, Bnai Zion Medical Center, Haifa, Israel; Sara Shapiro, Serology Laboratory, Carmel Medical Center, Haifa, Israel; Tamy Shohat, Israel Center for Disease Control, Tel Aviv, Israel; Eli Somekh, Wolfson Medical Center, Tel Aviv, Israel; Yossi Rimmar, Department of Clinical Microbiology, Bnai Zion Medical Center, Haifa, Israel; Vladimir Gershtein, Serology Laboratory, Carmel Medical Center, Haifa, Israel; Rosa Gershtein, Department of Clinical Microbiology, Bnai Zion Medical Center, Haifa, Israel; Esther Marva, Public Health Laboratories, Jerusalem, Israel; Nitza Lahat, Serology Laboratory, Carmel Medical Center, Haifa, Israel

Abstract

We tested 46 fully vaccinated children in two day-care centers in Israel who were exposed to a fatal case of pertussis infection. Only two of five children who tested positive for Bordetella pertussis met the World Health Organization's case definition for pertussis. Vaccinated children may be asymptomatic reservoirs for infection. [Emerging Infectious Diseases 6(5), 2000. Centers for Disease Control]

Introduction

Pertussis, an acute disease of the upper respiratory tract caused by the gram-negative bacillus Bordetella pertussis, lasts 6 to 8 weeks and has three clinical stages. The initial (catarrhal) stage resembles a common cold with a mild cough. The second (paroxysmal) stage is characterized by episodes of repetitive coughing during a single expiration, followed by a sudden inspiration that generates the typical "whoop." The final (convalescent) stage, which lasts 1 to 2 weeks, marks a decrease in the severity and frequency of the cough.

Since the introduction of routine childhood vaccine, pertussis has been considered preventable, and pertussis-associated illness and deaths are uncommon^[2]. However, vaccine-induced immunity wanes after 5 to 10 years, making the vaccinated host vulnerable to infection^[3]. This susceptibility has been described in outbreaks of pertussis infection in highly vaccinated populations^[3-6].

A recent study by Yaari et al. showed that infection in a vaccinated person causes milder, nonspecific disease, without the three classical clinical stages^[7]. Whooping cough is seen in only 6% of such cases; instead, the illness is characterized by a nonspecific, prolonged cough, lasting several weeks to months. Because of these atypical symptoms, pertussis infection is underdiagnosed in adults and adolescents, who may be reservoirs for infection of unvaccinated infants^[8-10]. In a study in France, up to 80% of infections in unvaccinated children were acquired from siblings and parents, suggesting that adults and even young siblings play a fundamental role in the transmission of pertussis^[11].

We demonstrated B. pertussis infection in fully vaccinated children ages 2-3 years and 5-6 years who had contact with an infected child. We investigated whether younger or recently vaccinated children may be protected from classical clinical illness but remain susceptible to infection and become asymptomatic carriers.

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Dr. Srugo is a senior lecturer and director of the Clinical Microbiology and Pediatric Infectious Disease unit at the Bnai Zion Medical Center, Haifa, Israel.

Address for correspondence: Isaac Srugo, Department of Clinical Microbiology, Bnai Zion Medical Center, POB 4940, Haifa, Israel 31048; Fax: 972-4-835-9614; e-mail: srugoi@tx.technion.ac.il