Notes From the Field: Pertussis—California, January–June 2010 FREE

MMWR. 2010;59:817

The number of pertussis cases reported to the California Department of Public Health (CDPH) has increased substantially during 2010. The increase in cases was first noted in late March among patients admitted to a children's hospital. During January 1– June 30, 2010, a total of 1,337 cases were reported, a 418% increase from the 258 cases reported during the same period in 2009. All cases either met the Council of State and Territorial Epidemiologists definitions for confirmed or probable pertussis or had an acute cough illness and Bordetella pertussis—specific nucleic acid detected by polymerase chain reaction from nasopharyngeal specimens.¹

During January—June in California, the incidence of pertussis was 3.4 cases per 100,000 population. County rates ranged from zero to 76.9 cases per 100,000 (median: 2.0 cases). By age group, incidence was highest (38.5 cases per 100,000) among infants aged <1 year; 89% of cases were among infants aged <6 months, who are too young to be fully immunized. Incidence among children aged 7-9 years and 10-18 years was 10.1 cases and 9.3 cases per 100,000, respectively.

Of 634 case reports with available data, 105 (16.6%) patients were hospitalized, of whom 66 (62.9%) were aged <3 months. Incidence among Hispanic infants (49.8 cases per 100,000) was higher than among other racial/ethnic populations. Five deaths were reported, all in previously healthy Hispanic infants aged <2 months at disease onset; none had received any pertussis-containing vaccines.

The incidence of pertussis is cyclical, with peaks occurring every 3-5 years in the United States.² The last peak was in 2005, when approximately 25,000 cases were reported nationally and approximately 3,000 cases in California, including eight deaths in infants aged <3 months. If the rates from the first half of the year persist throughout 2010, California would have its highest annual rate of pertussis reported since 1963 and the most cases reported since 1958.

CDPH is attempting to prevent transmission of pertussis to vulnerable infants³ by disseminating educational materials and clinical guidance, raising community awareness, and offering free tetanus, diphtheria, and acellular pertussis (Tdap) vaccine to birthing hospitals and local health departments to support postpartum vaccination of mothers and close contacts of newborns.

K Winter, MPH, K Harriman, PhD, R Schechter, MD, E Yamada, MD, J Talarico, DO, G Chavez, MD, California Dept of Public Health.