A cluster of tick-borne infections: association with military training and asymptomatic infections due to Rickettsia rickettsii.
During the spring of 1989, 86 members of a military unit from the state of Maryland, USA, participated in two-week-long training manoeuvres in the states of Arkansas (location FC) and Virginia (location FAPH). Acute febrile illnesses due to infections with two tick-borne pathogens, Rickettsia rickettsii and Ehrlichia sp., were confirmed serologically in 2 initial cases who were admitted to the hospital. A seroepidemiological investigation among unit members found an additional 17 of 109 individuals (16%) with elevated post-exposure indirect immunofluorescent antibody (IFA) titres to R. rickettsii (16 cases) and/or E. canis (2 cases). The seropositivity rate of personnel who trained at FC was 38% (15 of 40), compared to only 13% (4 of 31) and 8% (3 of 38) of personnel who trained at FAPH or who did not train in the field, respectively (P < 0.001). Seropositivity was associated with symptoms suggestive of a tick-borne illness. Only 4 (22%) and 6 (33%) of the 18 personnel seropositive for R. rickettsii reported an erythematous or petechial type of rash or a febrile illness, respectively, within 4 weeks of exposure; 5 of 18 (28%) personnel infected with R. rickettsii reported no symptoms and only 8 of 18 (44%) received medical treatment. Mild infections with R. rickettsii, or a closely related spotted fever group agent, may have accounted for the high infection rate experienced by this group.
Sanchez
J L
JL
Division of Preventive Medicine, Walter Reed Army Institute of Research, Washington, DC 20307-5100.
Candler
W H
WH
Fishbein
D B
DB
Greene
C R
CR
Coté
T R
TR
Kelly
D J
DJ
Driggers
D P
DP
Johnson
B J
BJ
D000907:Antibodies, Bacterial / Q000032:analysis; D001131:Arkansas / Q000453:epidemiology; D004536:Ehrlichia / Q000276:immunology; D006801:Humans; D008889:Military Personnel; D012284:Rickettsia rickettsii / Q000276:immunology; D012373:Rocky Mountain Spotted Fever / Q000453:epidemiology* / Q000276:immunology; D013984:Tick Infestations / Q000453:epidemiology*; D014768:Virginia / Q000453:epidemiology
D000907:Antibodies, Bacterial