Duration of Protection: GSK DTaP Vaccines

Inclusion Criteria: * Kaiser Permanente Northern California (KPNC) member who received 5 doses of acellular pertussis vaccines be-tween ages 1 month and 84 months at KPNC. * The 5th dose was given between the ages of 47 and 84 months. * All 5 DTaP doses received were manufactured by GSK, depending on study objective (otherwise this criterion will not apply). * Born in 1999 and later. Inclusion criteria for cases: • All individuals meeting above inclusion criteria who tested PCR-positive for pertussis and negative for parapertussis during the study period. Inclusion criteria for PCR-negative controls: • All individuals meeting above inclusion criteria who tested PCR-negative for both pertussis and parapertussis during the study period. Inclusion criteria for KPNC-matched controls: * All individuals from the general KPNC population meeting above inclusion criteria who match a PCR-positive case on sex, age, race or ethnic group, and medical center. * KPNC members on the day their matched case under-went the PCR test (anchor date). Exclusion Criteria: * Individuals whose PCR test date (or anchor date) is less than 2 weeks after receiving their 5th DTaP dose. * Individuals who were not KPNC members for greater than 3 months between their 5th DTaP dose and PCR test date (or anchor date). * Individuals who received reduced antigen content pertussis vaccine (Tdap) or any pertussis-containing vaccine after their 5th DTaP dose but before their PCR test date (or anchor date). Exclusion criteria for controls: • Individuals will be excluded from serving as a control once they test positive for pertussis.