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

Disclosures

Emerging Infectious Diseases. 2000;6(5) 

In This Article

Conclusions

The effects of whole-cell pertussis vaccine wane after 5 to 10 years, and infection in a vaccinated person causes nonspecific symptoms[3,4,5,6,7]. Vaccinated adolescents and adults may serve as reservoirs for silent infection and become potential transmitters to unprotected infants[3,4,5,6,7,8,9,10,11]. The whole-cell vaccine for pertussis is protective only against clinical disease, not against infection[15,16,17]. Therefore, even young, recently vaccinated children may serve as reservoirs and potential transmitters of infection.

We used PCR, EIA, and culture to confirm B. pertussis infection in two highly vaccinated groups of children in two day-care centers. Three (10%) of 30 2- to 3-year-old children were seropositive for recent infection; one had nasopharyngeal colonization and a clinical illness that met the modified WHO case definition. In the day-care center for the 5- to 6-year-old group, 9 (55%) of 16 children were IgM positive, 4 (25%) of whom had nasopharyngeal colonization. Of these four children, three had nonspecific cough, and only one met the modified WHO definition for pertussis. None of the children in our study, including those who met the WHO definition, had been examined by a physician before our investigation.

Children who were seropositive and remained both asymptomatic and PCR negative probably had sufficient immunity from vaccines or natural boosters to protect them against persistent colonization and clinical disease. Their seropositivity could not be due to vaccine because the children were tested more than a year after having been vaccinated. Yet not all the children were protected from infection and from colonization with the bacteria. Whether a child who is serologically or PCR positive for pertussis and is clinically asymptomatic is a potential transmitter of infection has not been established. What is certain, however, is that vaccine-induced immunity against infection does not persist throughout adulthood. In France, booster vaccinations have been recommended for adolescents and teenagers[18]. We found that immunity does not even persist into early childhood in some cases. We also observed that DPT vaccine does not fully protect children against the level of clinical disease defined by WHO. Our results indicate that children ages 5-6 years and possibly younger, ages 2-3 years, play a role as silent reservoirs in the transmission of pertussis in the community. More studies are needed to find the immunologic basis of protection against infection and colonization and thus an effective way to eradicate pertussis.

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