Serogroup Y meningococcal disease in Chicago, 1991-1997

Context.-In 1994, surveillance by the Chicago Department of Public Health d etected a growing trend in the proportion of invasive meningococcal infecti ons caused by serogroup Y. Objective.-To examine the emergence of serogroup Y meningococcal disease an d compare its clinical characteristics with those of other meningococcal se rogroups. Design.-Population-based retrospective review of surveillance records; medi cal record review and cohort analysis of serogroup Y vs non-serogroup Y cas e patients. Setting.-Chicago, Ill. Participants.-City residents with Neisseria meningitidis isolated from a no rmally 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 clin ical outcomes. Results.-We identified 214 case patients; 53 (25%) had serogroup Y. The att ack rate of serogroup Y meningococcal disease increased from 0.04 cases per 100 000 in 1991 to a peak of 0.82 cases per 100 000 in 1995 and subsequent ly decreased to 0.26 cases per 100 000 and 0.34 cases per 100 000 in 1996 a nd 1997, respectively. Compared with patients infected by other serogroups, patients with serogroup Y were older (median age, 16 years vs 1 year; P=.0 01) and more likely to have a chronic underlying illness (prevalence ratio, 2.3; 95% confidence interval, 1.2-4.4). Outcome did not differ significant ly between the 2 groups. Multilocus enzyme electrophoresis typing of isolat es from 19 case patients identified 5 different types. We found no clusteri ng among the enzyme types by age, race/ethnicity, community area, or time. Conclusions.-Serogroup Y emerged as the most frequent cause of meningococca l disease in Chicago in 1995 and accounted for a substantial proportion of cases in 1996 and 1997. Current data suggest that the magnitude of serogrou p Y meningococcal disease is sufficient for vaccine developers to incorpora te serogroup Y into new vaccines.