Epidemiologic Notes and Reports
Update: Arboviral Surveillance -- Florida, 1990
During the summer of 1990, surveillance of St. Louis encephalitis
(SLE) and eastern equine encephalitis viruses in vector
mosquitoes and avian hosts indicated a high level of viral
transmission in nature and a potential for epidemic transmission
in several states (1). The Florida Department of Health and
Rehabilitative Services initiated weekly active surveillance of
county public health units, hospitals, and clinical laboratories
in August after rising seroconversion rates were detected in
sentinel chickens. Since September 7, epidemic transmission of
SLE in central Florida has led to 12 additional confirmed or
presumptive cases in humans, bringing the total number of
laboratory-documented cases to 18; 52 additional suspected cases
are under investigation.
Suspected and laboratory-documented cases have been reported from
13 counties, with most reports from Indian River (51%), Orange
(12%), Brevard (10%), and Lake (7%) counties. The earliest onset
date for a laboratory-documented case was July 28, and onset of
illness for the most recent presumptive case was September 6.
Public warnings have been issued, and larviciding and aerial and
ground-based adulticiding have been intensified in the affected
areas.
Reported by: DL Wells, MD, E Buff, AL Lewis, RA Calder, MD, State
Epidemiologist, Florida Dept of Health and Rehabilitative Svcs.
Div of Vector-Borne Infectious Diseases, Center for Infectious
Diseases; Div of Field Svcs, Epidemiology Program Office, CDC.
Editorial Note
Editorial Note: The 18 laboratory-documented SLE cases reported
from Florida in 1990 constitute the largest outbreak in the state
since 1977, when 110 laboratory-documented cases were reported
from the same central counties (2). Additional cases may occur
because SLE viral transmission in Florida usually peaks in early
October (3). Furthermore, in the fall, the principal mosquito
vector of SLE in the state, Culex nigripalpus, shifts its host
feeding preference from avians to mammals (4).
Nelson DB, Kappus KD, Janowski HT, Buff E, Wellings FM,
Schneider NJ. St. Louis encephalitis--Florida, 1977, patterns of
a widespread outbreak. Am J Trop Med Hyg 1983;32:412-6.
Monath TP, Tsai TF. St. Louis encephalitis: lessons from the
last decade. Am J Trop Med Hyg 1987;37(suppl):40S-59S.
Edman JD, Taylor DJ. Culex nigripalpus: seasonal shift in the
bird-mammal feeding ratio in a mosquito vector of human
encephalitis. Science 1968;161:67-8.
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