To assess the impact of Bordetella pertussis infections in South Australia during an epidemic and determine vulnerable populations, data from notification reports for pertussis cases occurring between July 2008 and December 2009 were reviewed to determine the distribution of disease according to specific risk factors and examine associations with hospitalizations. Although the majority (66%) of the 6230 notifications for pertussis occurred in adults aged >24 years, the highest notification and hospitalization rate occurred in infants aged <1 year. For these infants, factors associated with hospitalization included being aged <2 months [relative risk (RR) 2·3, 95% confidence interval (CI) 1·60-3·32], Indigenous ethnicity (RR 1·7, 95% CI 1·03-2·83) and receiving fewer than two doses of pertussis vaccine (RR 4·1, 95% CI 1·37-12·11). A combination of strategies aimed at improving direct protection for newborns, vaccination for the elderly, and reducing transmission from close contacts of infants are required for prevention of severe pertussis disease.