Context: In 1994, surveillance by the Chicago Department of Public Health detected a growing trend in the proportion of invasive meningococcal infections caused by serogroup Y.
Objective: To examine the emergence of serogroup Y meningococcal disease and compare its clinical characteristics with those of other meningococcal serogroups.
Design: Population-based retrospective review of surveillance records; medical record review and cohort analysis of serogroup Y vs non-serogroup Y case patients.
Setting: Chicago, III.
Participants: City residents with Neisseria meningitidis isolated from a normally sterile site from January 1, 1991, through December 31, 1997; cohort analysis included those identified through March 31, 1996.
Main outcome measures: Serogroup-specific incidence, demographics, and clinical outcomes.
Results: We identified 214 case patients; 53 (25%) had serogroup Y. The attack rate of serogroup Y meningococcal disease increased from 0.04 cases per 100000 in 1991 to a peak of 0.82 cases per 100000 in 1995 and subsequently decreased to 0.26 cases per 100000 and 0.34 cases per 100000 in 1996 and 1997, respectively. Compared with patients infected by other serogroups, patients with serogroup Y were older (median age, 16 years vs 1 year; P = .001) and more likely to have a chronic underlying illness (prevalence ratio, 2.3; 95% confidence interval, 1.2-4.4). Outcome did not differ significantly between the 2 groups. Multilocus enzyme electrophoresis typing of isolates from 19 case patients identified 5 different types. We found no clustering among the enzyme types by age, race/ethnicity, community area, or time.
Conclusions: Serogroup Y emerged as the most frequent cause of meningococcal disease in Chicago in 1995 and accounted for a substantial proportion of cases in 1996 and 1997. Current data suggest that the magnitude of serogroup Y meningococcal disease is sufficient for vaccine developers to incorporate serogroup Y into new vaccines.