Shigellosis among swimmers in a freshwater lake.
OBJECTIVE
Shigella infection is highly communicable; however, outbreaks associated with swimming in recreational fresh water are rarely identified.


METHODS
A cohort study of lake visitors was performed.


RESULTS
Seventeen (24.6%) case patients among 69 persons who visited the lake over the holiday weekend were identified. Attack rates increased with increasing exposure to lake water; the risk of illness was greatest among swimmers who reported getting lake water in their mouths (relative risk = 5.37, 95% confidence interval = 2.2, 13.3). Shigella sonnei was isolated from stool samples of four of eight swimmers tested.


CONCLUSIONS
The outbreak likely was caused by fecal contamination of lake water by an infected swimmer; there was no evidence of sewage contamination into the lake. Fresh water is a potential source of infection in patients with acute gastroenteritis and recent exposure. Since testing and chlorination of lake water is impractical, prevention relies on avoidance of fecal contamination and/or minimizing ingestion of the water.
Iwamoto
Martha
M
Epidemic Intelligence Service, Epidemiology Program Office, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA. miwamoto@cdc.gov
Hlady
Gary
G
Jeter
Monica
M
Burnett
Cindy
C
Drenzek
Cherie
C
Lance
Susan
S
Benson
James
J
Page
David
D
Blake
Paul
P
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D004196:Disease Outbreaks; D004405:Dysentery, Bacillary / Q000453:epidemiology* / Q000517:prevention & control / Q000635:transmission; D005260:Female; D005618:Fresh Water / Q000382:microbiology*; D005845:Georgia / Q000453:epidemiology; D006801:Humans; D007223:Infant; D008875:Middle Aged; D012764:Shigella sonnei; D013550:Swimming