AN OUTBREAK OF LEPTOSPIROSIS AMONG PERUVIAN MILITARY RECRUITS

KEVIN L. RUSSELL 0 MARCO A. MONTIEL GONZALEZ 0 DOUGLAS M. WATTS 0 ROBERTO C. LAGOS-FIGUEROA 0 GLORIA CHAUCA 0 MARIANELA ORE 0 JOSE E. GONZALEZ 0 CECILIA MORON 0 ROBERT B. TESH 0 JOSEPH M. VINETZ 0 0 United States Naval Medical Research Center Detachment , Lima, Peru ; Department of Infectious Diseases, Military Hospital , Lima, Peru ; Technical School , Peruvian Army, Lima, Peru ; Center for Tropical Diseases, Department of Pathology, University of Texas Medical Branch , Galveston, Texas Acute undifferentiated febrile illnesses are common in tropical developing countries but are difficult to diagnose on clinical grounds alone. Leptospirosis is rarely diagnosed, despite evidence that sporadic cases and epidemics continue to occur worldwide. The purpose of this study was to diagnose an outbreak of acute undifferentiated febrile illness among Peruvian military recruits that developed after a training exercise in the high jungle rainforest of Peru. Of 193 military recruits, 78 developed anacute febrile illness with varied m anifestations. Of these, 72 were found to have acute leptospirosis by a microscopic agglutinationtest (MAT). Anenzyme -linked immunosorbent assay using Leptospira biflexa antigen was insensitive for the detection of anti-leptospiral IgM antibodies compared with the MAT (20 of 72, 28%). This outbreak of acute undifferentiated febrile illness among Peruvianmilitary recruits was due to leptospirosis. High clinical suspicion, initiation of preventative measures, and performance of appropriate diagnostic testing is warranted in similar settings to identify, treat, and prevent leptospirosis. - Several outbreaks of leptospirosis inrecent years have highlighted the global importance of this widespread zoonotic disease.14 The spirochetes that cause leptospirosis are transmitted to humans from a variety of chronically infected peridomestic mammalianreservoir hosts such as rodents, cattle, pigs, and dogs, as well as potentially from wild mammals such as rodents, marsupials, and bats.5,6 Humans become infected either through percutaneous or mucosal exposure to infected urine or ground waters containing leptospires. Infected mammals shed leptospires from renal tubules where the organisms canpersist for months to years. 5 Pathogenic leptospires are enzootic throughout tropical regions including Peru.6,7 Risk factors for leptospirosis include living in rural and tropical settings with exposure to leptospire-contaminated fresh water and agriculture, sewer, and sanitation work; military personnel are also regarded as at-risk because of field activities that bring them into close contact with zoonotic reservoirs.810 However, these same patient populations are also frequently at risk for a variety of other infections that can manifest as acute, undifferentiated febrile or influenza-like illnesses. On clinical grounds alone, it is often difficult to distinguish among the many causes of acute undifferentiated febrile illness inthe tropics, which caninclude malaria, arboviruses such as dengue, rickettsioses such as scrub typhus, or ehrlichiosis. Here we show how a systematic, comprehensive approach led to the identification of leptospirosis as the cause of an outbreak of acute undifferentiated febrile illness that occurred among military recruits participating in training exercises ina high jungle regionof Peru. The performance of a commercially available enzyme-linked immunosorbent assay (ELISA) for the diagnosis of leptospirosis was also evaluated inthis outbreak. MATERIALS AND METHODS From March to May 1999, 193 Peruvianmilitary recruits accompanied by 25 officers and support personnel attended a training exercise in the high Amazonian jungle near the city of Pichanaqui (Chanchamayo Province, Junin Department), Peru (Figure 1). This is a farming region where a variety of agricultural and animal products are produced. Although not the rainy season, occasional rainstorms occurred during this hot, humid summer period with anaverage temperature of 22C. No flooding was experienced during this period. Recruits received a yellow fever vaccination three days prior to arrival at the training site; officers and support personnel had been vaccinated previously. The recruits spent two weeks in the area. During a period of approximately four weeks after the training period, 78 of the 193 recruits were hospitalized in Lima, Peru with an acute undifferentiated febrile illness. Some cases were probably missed since recruits that did not report to the hospital were unavailable for questioning. A standard questionnaire was used to obtain demographic information, exposure history to animals and various sources of ground water, and clinical data from all 78 of the hospitalized recruits and from 14 of the 25 healthy support staff. A case was defined as any individual present during the training exercises who reported to the hospital with anacute febrile illness during the month following the completion of the exercise. Acute blood samples were obtained from the 78 hospitalized recruits and from 14 healthy support staff; convalescent samples were drawn three weeks later. None of the healthy recruits were available for sampling. An IgM ELISA was used to test all acute and convalescent sera for evidence of acute infection to the following arboviruses: dengue, Oropouche, Venezuelan equine encephalitis (VEE), Mayaro, and yellow fever.1113 Acute sera were tested for virus in cultures of Vero and C6/36 cells by standard procedures. Immunofluorescence was performed on all cell cultures using polyclonal antibodies against dengue, yellow fever, Mayaro, VEE, Oropouche, and group C bunyaviridae viruses.12 The sera were also examine for antibodies against rickettsial and ehrlichial species using an immunofluorescence test previously described.14 Convalescent serum samples were screened for antileptospiral IgM antibodies using a Leptospira biflexa antigen ina commercial ELISA kit (Leptospira IgM ELISA Test, catalogue no. LPM-200; Pan Bio, Gaithersburg, MD). Acute samples were also tested from patients that tested positive for IgM antibodies in their convalescent sera. The microscopic agglutination test (MAT) was used as the gold standard, and included a standard panel of 23 leptospiral serovars representing the known pathogenic serogroups.5 The MAT results were interpreted as definitely positive with a four-fold or higher increase in antibody titer, a single titer 1/800, or conversion from negative to positive between the acute and convalescent samples; probably positive was defined as a titer 1/400 with either no change or less than a four-fold increase intiter betweenthe paired samples. These criteria are consistent with those in the published literature.5,1517 Potential exposures to infectious pathogens were similar for recruits and the support staff with the exception of the recruits sleeping location, common latrine location, and certain training exercises. Each day the recruits swam in (...truncated)