The purpose of this study is to assess duration of protection for GSK DTaP vaccines in preventing pertussis.

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.

Kaiser Permanente Northern California (KPNC) member who received 5 doses of acellular pertussis vaccines between ages 1 month and 84 months at KPNC.