Pertussis Cases Near 10,000 in California This Year

Laurie Barclay, MD

December 04, 2014

Through November 26, there were 9935 cases of pertussis with onset in 2014 reported in California, according to a surveillance report published in the December 5 issue of the Morbidity and Mortality Weekly Report. This epidemic (26.0 cases per 100,000 population), as well as severe and fatal disease occurring almost exclusively in infants who are too young to be vaccinated, highlights the need for vaccination of pregnant women in their third trimester.

"In the prevaccine and postvaccine eras, pertussis incidence has been cyclical and peaks every 3–5 years," write Kathleen Winter, MPH, from the Immunization Branch, California Department of Public Health, Richmond, and colleagues. "Incidence of reported pertussis has been increasing in the United States since the 1980s despite widespread use of pertussis vaccines. Large outbreaks of pertussis occurred in California in 2010 and in other states during 2011–2012."

Because of the natural cycle of pertussis and waning immunity offered by currently available vaccines, pertussis incidence in the United States is likely to continue to rise. On June 13, 2014, the California Department of Public Health noted that reported incidence of pertussis was more than fivefold greater than baseline levels, and therefore declared a pertussis epidemic in California.

Infants younger than 12 months, and particularly Hispanic infants, have the highest burden of disease, along with white, non-Hispanic teenagers aged 14 to 16 years. The latter group represents the cohort of children who received only acellular pertussis vaccine. In the former group, the rate ratio of pertussis incidence for Hispanic vs non-Hispanic infants was 1.7 (95% confidence interval, 1.5 - 2.1).

Because of the high risk for infants who are too young to be vaccinated against the disease, strategies to prevent cases in this age group (those younger than 2 months) should receive the highest priority.

To ensure placental transfer of maternal antibodies to the infant, women should receive tetanus, diphtheria, and acellular pertussis vaccine (Tdap) during the third trimester of each pregnancy, as recommended by the Advisory Committee on Immunization Practices. However, only 17% of mothers of infants diagnosed with pertussis in California in 2014 reported receiving Tdap during the third trimester of pregnancy.

Clinicians caring for pregnant women should therefore provide them with Tdap, which is considered best practice, or refer them to obtain vaccine from a pharmacy, local public health department, or other alternative provider.

"Prevention efforts should be focused on preventing severe disease and death from pertussis in young infants," the report authors write. "The preferred strategy is vaccination of pregnant women during the third trimester of each pregnancy to provide placental transfer of maternal antibodies to the infant.... Efforts should be made to eliminate barriers to receiving vaccines from prenatal care providers."

The authors have disclosed no relevant financial relationships.

Morb Mortal Wkly Rep. 2014;63:1129-1132.

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