Hantavirus Pulmonary Syndrome -- Chile, 1997

Hantavirus pulmonary syndrome (HPS) * was first recognized in Chile in October 1995; through July 1997, nine cases had been identified in the country. However, during August 1-October 8, 1997, a total of 12 persons with HPS, including two family clusters, were recognized. A collaborative investigation is under way to determine the magnitude of this outbreak, the associated rodent reservoir for hantaviruses, and the major risk factors for human infection. This report summarizes the preliminary results of the ongoing investigation, which suggest that the outbreak among humans is paralleled by exceptionally high densities of potential rodent reservoir species.

From October 4, 1995, through October 8, 1997, a total of 21 HPS case patients were identified in Chile; 13 died (case-fatality proportion: 62%). The mean age of patients was 26 years (range: 1 year 11 months to 41 years); four (19%) of the cases were in children aged less than 17 years; 76% of cases were in males. No cases occurred among health-care workers. The outbreak that began in August 1997 is centered in two southern regions of Chile (population: 1.1 million). Genetic sequencing of material amplified from the autopsy tissue of one case-patient presumptively infected in one of these two regions identified Andes virus as the etiologic agent (2). Clinical features have been similar to those reported in North America (3) but have included at least three children with petechiae.

The first family cluster (cluster 1) of HPS was reported from Cisne Medio, Lago Verde community, Aysen region. On July 15, a 39-year-old man (index case) had onset of an acute febrile respiratory illness; he died on July 21, but no appropriate specimens were available for laboratory diagnosis of HPS. Except for a brief visit to the family's house on July 27 to retrieve personal belongings, family members moved to a house in a village 4.4 miles (7 km) away. Onsets of laboratory-confirmed cases of HPS occurred in the index case-patient's wife (August 2), 2-year-old son (August 9), 12-year-old son (August 18), and his brother-in-law (who intermittently stayed in the original residence) (September 5). The second family cluster (cluster 2) included three of the four members of a household in Lago Atravesado, Coyhaique community, Aysen region. All case-patients had onsets of illness during August 23-28.

A total of 569 rodent traps were placed at the original residence of cluster 1 (on the night of August 27), at the residence of cluster 2 (on the nights of August 28 and 29), at two neighboring controls (within 889 yards {800 m}) of each case-household, and in a forested area near Lago Atravesado. Trapping yielded 253 rodents, of which 119 (47%) were Oligoryzomys longicaudatus; the remainder primarily were Akodon olivaceous and Akodon (Abrothrix) longipilus. High trap success in the forested area (22 {55%} captures in 40 traps) indicated that high rodent densities were not restricted to peridomestic areas. The overall trap success in the Aysen region was approximately five times that achieved 375 miles (600 km) north in Paillaco, 21.9 miles (35 km) southwest of Valdivia (49 {10%} of 478 traps).

Reported by: R Murua, DVM, Austral Univ, Valdivia; B Barra, JL Vera Mora, H Villalon, MD, C Mansilla, MD, M Tapia, MD, JJ Chaparro, MD, F Torres, MD, Coyhaique Regional Hospital; J Barria, G Aguila, P Escobar, N Gallegos, R Valderrama, MD, J Montecinos, MD, Director, Aysen Health Svcs, Coyhaique; K Mardoff, R Mansilla, DVM, Valdivia Health Svcs, Valdivia; JA Vergara, MD, Llanchipal Health Svcs, Puerto Montt; C Pavletic, DVM, J Toro, MD, A Figueroa, MD, Minister of Health, Ministry of Health; R Cerda, J Vega, MD, R Penna, MD, Pan American Health Organization, Santiago, Chile. G Calderėn, H Lopez, D Enria, MD, National Institute of Human Viral Diseases, Pergamino; P Padula, PhD, National Institute of Infectious Diseases; Z Yadon, MD, E Segura, PhD, National Administration of Laboratories and Institutes of Health, Malbran, Buenos Aires, Argentina. Viral and Rickettsial Zoonoses Br, Infectious Disease Pathology Activity, and Special Pathogens Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Since its initial description in 1993, HPS has been established as a pan-American zoonosis (4). The basic clinical features in humans include fever, headache, myalgia, and gastrointestinal symptoms, followed by noncardiogenic pulmonary edema, cardiovascular collapse, and a 40%-60% case-fatality proportion. HPS results from infection with New World hantaviruses that are maintained by a single rodent reservoir species belonging to the subfamily Sigmodontinae (Order: Rodentia; Family: Muridae). Infection and disease in humans can occur after exposure to aerosols of secretions and excretions from infected rodents. Approximately 400 cases have been detected throughout the Americas, with retrospective cases identified as early as 1959. Although most cases occur sporadically in areas with endemic disease throughout the Americas, periodic outbreaks, such as the current episode in Chile, intermittently occur in association with meteorologic and ecologic conditions that facilitate increased rodent densities and contact of rodents with humans.

Compared with features of HPS in the United States, distinctive features of the outbreak in Chile include the high proportion of cases among children and the common occurrence of a bleeding diathesis (3,4). The high trap success in Chile reflects the high population densities of rodents, especially O. longicaudatus, the species provisionally identified as the reservoir of Andes virus in southern Argentina (5). In previous outbreaks in Argentina, person-to-person transmission of Andes virus was documented (6,7). Although person-to-person transmission cannot be excluded as a factor for cluster 1, the high rodent population levels probably were associated with an increased frequency of human-rodent contact and, therefore, an increased risk for transmission of rodentborne hantaviruses to humans. Additional studies are being conducted to determine the major risk factors for human infection. This multidisciplinary investigation is coupled with training in specialized diagnostic techniques at CDC, training in rodent sampling protocols in the field, and transfer of diagnostic capability to Chile. Interim measures initiated by the Ministry of Health and the regional health services include a public health education campaign about methods for reducing rodent contact (8).

References

1. CDC. Case definitions for infectious conditions under public health surveillance. MMWR 1997;46(no. RR-10).

2. Lėpez N, Padula P, Rossi C, et al. Genetic characterization and phylogeny of Andes virus and variants from Argentina and Chile. Virus Res 1997;50:77-84.

3. Khan AS, Khabbaz RF, Armstrong LR, et al. Hantavirus pulmonary syndrome: the first 100 US cases. J Infect Dis 1996;173:1297-303.

4. Khan AS, Ksiazek TG, Peters CJ. Hantavirus pulmonary syndrome. Lancet 1996;347:739-41.

5. Levis SL, Morzunov SP, Rowe JE, et al. Genetic diversity and epidemiology of hantavirus in Argentina. J Infect Dis 1997(in press).

6. Enria D, Padula P, Segura EL, et al. Hantavirus pulmonary syndrome in Argentina. Possibility of person-to-person transmission. Medicina (Buenos Aires) 1995;58:709-11.

7. Wells RM, Estani SS, Yadon ZE, et al. An unusual hantavirus outbreak in southern Argentina: person-to-person transmission? Emerg Infect Dis 1997;3:171-4.

8. CDC. Hantavirus infection -- southwestern United States: interim recommendations for risk reduction. MMWR 1993;42(no. RR-11).

* HPS is defined as fever (greater than 101 F {38.3 C}), bilateral diffuse pulmonary edema, respiratory compromise requiring supplemental oxygen developing within 72 hours of hospitalization in a previously healthy person (1).

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