From 1988 to 2004, 545 cases of MD occurred in Oklahoma; 71 (13.0%) died. The number of cases ranged from 10 to 51 per year. The mean annual incidence rate during this time for Oklahoma and the U.S. was 1.0/100,000 population. The mean annual incidence rate from 2002 to 2004 (0.58) was 26.0% below the rate from 1988 to 1990 (0.78). One instance of secondary transmission in a household (two cases) occurred in 1992. One organization-based outbreak associated with a church occurred in 2000. Two confirmed cases and one probable case were associated with the cluster (age range 8 to 13 years, one female, two males). An isolate for serogrouping was available for one case, from which group C was identified. No deaths were associated with the outbreak. No community-based outbreaks were observed.
Age at onset ranged from <1 year of age to 99 years of age (mean 22.6 years, median 10 years). Infants younger than 1 year of age represented 18.2% of cases (annual rate 16.5/100,000) and nearly one-quarter occurred among children 0–23 months of age; the mean annual rate among children 0–23 months of age was significantly higher than among all other age groups (). Among people older than 14 years of age, adults aged 65 and older had a significantly higher incidence rate. The rate among males was 22.0% higher than among females (1.1 vs. 0.9 per 100,000, respectively) but was not statistically different. While the rate among people in urban areas was 22.0% higher than in rural areas, this was not statistically significant.
Meningococcal disease by outcome and selected demographic characteristics, Oklahoma, 1988–2004
Data on race were available for 487 (89.4%) cases. The rate among black individuals (1.28/100,000) was significantly higher than among white individuals (0.91/100,000) and Native Americans (0.57/100,000). The rate among Native Americans was not significantly different from white individuals. One case occurred in a person of Asian race. White residents had the highest rates among children 0 to 4 years of age and people aged 65 years and older; black individuals had the highest rates in all other age categories (). The rate among black males was significantly higher than among other race-gender groups (). Black males aged 4 years and older had the highest incidence of disease in all age groups and followed a different disease age distribution than the other race-gender groups; it was the only race-gender group in which rates increased in the 15–24 and 45–54 age groups and did not increase in the 65+ age group (). However, individual cell sizes were too small to determine if this distribution was significantly different from other races.
Rates of meningococcal disease by race and age group, Oklahoma, 1988–2004
Case-fatality rates (CFRs) varied from a high of 24.0% (six of 25) in 2003 to 3.9% (one of 26) in 1988. The five-year mean CFR from 1988 to 1992 was 11.1% as compared with 15.0% from 2000 to 2004; this difference was not statistically significant. People aged 40 years and older were 81% more likely to die than people younger than 40 years of age (rate ratio [RR] 1.81, 95% CI 1.18, 2.79). The CFR among rural cases was one-third higher than among urban cases, although it did not reach statistical significance (RR 1.33, 95% CI 0.74, 2.39).
Of 516 confirmed cases of MD, 115 (22.3%) did not have N. meningitidis isolates available for serogrouping at the OSDH laboratory. Of those that were provided to the OSDH laboratory, 122 (30.4%) were found to be serogroup B, 113 (28.2%) were serogroup C, 93 (23.2%) were serogroup Y, 15 (3.7%) were serogroup W-135, and one (0.3%) was serogroup X; 57 (14.2%) were not able to be grouped. Prior to 1993, serogroup Y had only been isolated once, while 33.3% of isolates since 1994 were serogroup Y. No other shifts in serogroup were noted. Fatality rates by serogroup were W-135 (33.3%), Y (18.3%), C (15.0%), and B (10.7%). These differences did not reach statistical significance (Fisher's exact test comparing W-135 vs. others combined, p=0.059).
Among groupable isolates obtained between 1988 and 2004, 60.8% of infants younger than 2 years of age were found to have serogroup B, followed by C (24.1%), Y (7.6%), and W-135 (7.6%). Serogroup C was the most common serogroup in people aged 2 to 39 years (48.1%), followed by B (33.3%), Y (12.9%), and W-135 (2.7%). Among people aged 40 years and older, serogroup Y was found to be the most common (54.6%), followed by B (23.2%), C (17.6%), and W-135 (4.6%). No differences in serogroup were noted by sex or race.
Forty-six MD cases matched with the hospital discharge database from 2002 to 2004. The mean length of hospital stay was 12 days (median eight days, range one to 128 days). Total hospital charges were more than $1.7 million. Mean hospital charges were $37,724 (median $18,393, range $776 to $269,367). Nearly three-quarters (72.0%) of people were discharged home, 11.0% were discharged to home health care, 7.0% died, 4.0% each were discharged to another acute care hospital or intermediate care facility, and 2.0% went to a rehabilitation center. Two people with meningococcemia and one person with Waterhouse-Friderichsen syndrome required amputations. Insurance was the primary payor for 44.0% of hospitalized people, followed by Medicaid (37.0%), self-pay (11.0%), Medicare (7.0%), and other government health care (2.0%).
Age and season of onset were the only variables found to predict death as an outcome measure in the logistic regression model. Race, sex, specimen source, year of onset, urban vs. rural residence, and serogroup were not found to be significant contributors for risk of death from MD. Older age at onset was associated with a higher likelihood of dying; for every 10 years of age, the risk of death increased 13.0% (adjusted odds ratio [AOR] 1.13, 95% CI 1.05, 1.22). Season of onset between October and February () was associated with greater risk of death than disease onset during the rest of the year (AOR 2.53, 95% CI 1.47, 4.33). Upon testing for interaction, the significance between age and season was 0.07. We then stratified our analysis by age <40 and ≥40 years. People younger than age 40 who developed MD between October and February () were 68.0% more likely to die than those younger than age 40 who became ill in other months (RR 1.68, 95% CI 1.39, 2.05); the increased risk of death during these months was elevated but not statistically significant in those aged 40 and older (RR 1.19, 95% CI 0.83, 1.69).
Meningococcal disease by month of onset and outcome, Oklahoma, 1988–2004
Meningococcal disease death rates by age group and season of onset, Oklahoma, 1988–2004