Pertussis on the Rise

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Summary and Comment

Pertussis on the Rise

Pertussis reached epidemic proportions in Washington State in 2012, apparently because of waning immunity in individuals who received acellular vaccines during childhood.

Pertussis incidence has been increasing since mid-2011 in the state of Washington. The number of cases reported in early 2012 — 2520 — was 1300% higher than the number during the same period in 2011. Rates were highest among infants aged <1 year, children aged 10 years, and adolescents fully vaccinated with tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine. Incidence among Hispanics was more than twice that among non-Hispanics (53.1 vs. 24.6 cases per 100,000 population).

A total of 2069 cases were confirmed by laboratory testing (83%) or epidemiologic linking (17%). Multitarget polymerase chain reaction (PCR) assays, performed on 193 specimens in which Bordetella DNA had been detected by PCR, identified B. pertussis in 175 (91%) and B. parapertussis in 11 (6%). Thirty (55%) of the 55 isolates subjected to pulsed-field gel electrophoresis represented the four most commonly identified profiles in the CDC's national database.

Valid vaccination history was available for 91% of the patients aged 3 months to 19 years. Seventy-six percent of the patients aged 3 months to 10 years were up to date with childhood diphtheria and tetanus toxoids and acellular pertussis doses; 43% of those aged 11 to 12 years and 77% of those aged 13 to 19 years had received the Tdap vaccine recommended for older children and adults.

Although the incidence of pertussis nationwide in early 2012 was far lower than that in Washington State (4.2 vs. 37.5 cases per 100,000), it also peaked among infants and among children aged 10, 13, and 14 years. Across the U.S., the case fatality rate showed a slight decrease from the previous decade.

Comment: Acellular vaccines replaced the older whole-cell products because of adverse events associated with the latter. It now appears that protection by the acellular vaccines, although lasting several years, may wane, leaving large populations unprotected against pertussis. Nonetheless, vaccination and revaccination remain the primary shields against infection.

— Stephen G. Baum, MD

Published in Journal Watch Infectious Diseases August 1, 2012

Citation(s):

Centers for Disease Control and Prevention (CDC). Pertussis epidemic — Washington, 2012. MMWR Morb Mortal Wkly Rep 2012 Jul 20; 61:517.

Medline abstract (Free)

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