Non-Medical Exemptions One Factor in Pertussis Resurgence

Spatial clustering of NMEs seen in California in 2010; linked with clusters of pertussis cases

Non-Medical Exemptions One Factor in Pertussis Resurgence

MONDAY, Sept. 30 (HealthDay News) -- Non-medical exemptions (NMEs) are likely to have been one of the factors that contributed to the resurgence of pertussis in California in 2010, according to a study published online Sept. 30 in Pediatrics.

Jessica E. Atwell, M.P.H., from the John Hopkins Bloomberg School of Public Health in Baltimore, and colleagues analyzed NMEs for children entering kindergarten from 2005 to 2010 and pertussis cases with onset in 2010 in California. The authors sought to examine whether clustering of unvaccinated individuals played a role in the resurgence of pertussis cases in California in 2010.

Based on Kulldorff's scan statistics, the researchers identified 39 significant clusters of high NME rates and two clusters of pertussis cases. The likelihood of being in a pertussis cluster was significantly increased for census tracts within an exemption cluster (odds ratio, 2.47). More cases occurred within versus outside exemption clusters (incident odds ratio, 1.20). After adjustment for demographic factors, the correlation was still significant. Spatial clustering of NMEs was observed and these correlated with clusters of pertussis cases.

"Our findings suggest that communities with large numbers of intentionally unvaccinated or undervaccinated persons can lead to pertussis outbreaks," the authors write. "In the presence of limited vaccine effectiveness and waning immunity, sustained community-level transmission can occur, putting those who are most susceptible to communicable diseases, such as young infants, at increased risk."

Two authors disclosed financial ties to the pharmaceutical industry.

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