Seasonality of the Top Four Vibrio Species By Transmission Route, United States, 1988–2012

BACKGROUND:   Approximately 80,000 Vibrio infections (vibriosis) occur annually in the United States. Vibrio bacteria inhabit marine and estuarine environments, proliferating when waters are warmer. While illness can occur throughout the year, overall incidence is higher between April and October and peaks during the summer months. A detailed assessment of seasonality of foodborne and non-foodborne transmitted vibriosis could help direct prevention efforts.  

METHODS:   CDC compiles cases reported nationally to the Cholera and Other Vibrio Illness Surveillance (COVIS) system, which collects information on patient demographics, specimen source, clinical illness, and exposures. We analyzed COVIS data from 1988 through 2012. Reported specimen sites (e.g., gastrointestinal) and exposures (e.g., seafood consumption) were categorized using a hierarchy to classify cases as foodborne or non-foodborne transmission. Analyses were limited to the four species most frequently reported to COVIS. Toxigenic V.choleraeO1 and O139 cases and patients that reported foreign travel were excluded.  When reported illness onset date was not available, month of illness onset was determined by specimen collection date. Radar plots for the top four species were constructed for each transmission route to examine seasonality.

RESULTS:   From 1988 through 2012, 10,173 domestically-acquired vibriosis cases were reported. The top four species (n=8452; 84%) were V. parahaemolyticus (n=4,224; 42%), V. vulnificus (n=1,998; 20%), V. alginolyticus (n=1,267; 13%), and V. cholerae (n=963, 9.5%). Among the top four species, 4,690 (56%) cases were foodborne, 2,885 (34%) were non-foodborne, and 877 (10%) could not be classified. For V. parahaemolyticus, foodborne cases (80%) peaked in July (25%) and August (26%); non-foodborne cases (17%) peaked in July (22%). For V. vulnificus, both foodborne (30%) and non-foodborne (44%) cases peaked in August (19% and 23%, respectively); unlike foodborne cases, non-foodborne cases increased markedly from May (9.1%) to July (19%). For V. alginolyticus, foodborne cases (7.7%) peaked in June (14%) and July (14%); non-foodborne cases (85%) peaked in July (18%) and August (18%). For V. cholerae,foodborne cases (65.9%) were highest in the month of May (14%), but remained high in June (15%) and July (14%); non-foodborne cases (20%) peaked in August (21%)

CONCLUSIONS:   COVIS data reinforce the well-known peak in overall vibriosis incidence during summer months when waters are warmest. However, there was variability in the relative frequency of case reports by species and transmission route among the top four reported Vibrio species. Therefore, prevention programs may be most effective when timed to precede peaks in seasonality and focused specifically on transmission route.