To the Editor: After more than 70 years without reports of cases, an outbreak of dengue (type 2) occurred in the northwestern region of Argentina from January to May 1998; 818 cases of dengue-like illness were reported (incidence rate: 45/10,000 inhabitants) (1). The outbreak was restricted to a few cities of the Chaco Salteño Region.

The last dengue epidemic in Argentina (in 1926) (2), affected the Mesopotamia Region and Rosario City. An earlier widely distributed epidemic in 1916 occurred in the coastal region along the Uruguay River (Corrientes and Entre Ríos provinces), reached Parana City (along the Parana River), and affected approximately 50% of the city’s population (3). Both outbreaks began in Paraguay. No cases were detected in Buenos Aires.

High numbers of Aedes aegypti are reported in all places where surveillance for these vectors is conducted in Argentina. The Breteau rate (a measure of vector density; the number of positive containers is divided by the number of inspected houses) in the Federal District averaged >40% in the first trimester of 2000 and was 30% to 80% in suburban districts in 1999 (R. Boffi, Ministerio de Salud de la Nación; N. Schweigmann, University of Buenos Aires, pers. commun.).

In Argentina’s neighboring countries, dengue is a serious public health problem. From December 1999 through March 2000, Paraguay reported 42,000 dengue cases, 9 of hemorrhagic dengue fever (4). Brazil has reported cases of dengue and hemorrhagic dengue fever, and Bolivia has reported dengue and a large yellow fever outbreak (4). From December 1999 to March 2000, 85 patients with dengue-like illness arrived in Buenos Aires from one of these countries’ dengue-epidemic areas and were seen at F. J. Muñiz Hospital in Buenos Aires. An enzyme-linked immunosorbent assay-capture immunoglobulin M test (commercial kit) (5) and a plaque reduction neutralization test on cell culture were performed (6). Laboratory diagnosis of dengue infection was made in 38 cases. Twenty-five cases were in female patients, and 13 were in male patients; the age of patients was 8 to 74 years (average, 39 years). All patients were Argentinean residents; 18 (47.4%) lived in the Federal District, and 20 (52.7%) in the suburban area (west and south). Except for one patient who had traveled to Saint Thomas Island, the patients traveled from Paraguay (Asunción, Ciudad del Este, Luque, and other cities). The patients had been out of Argentina 4 to 60 days (average, 17 days). Twenty-six (68.4%) patients had viremia in their place of residence (Federal District or suburbs). In Buenos Aires, 20 patients had viremia for 5 days, 3 patients for 4 days, and 3 patients for 3 days. Ten patients (26.3%) had mild febrile illness; 23 (57.1%) had classic dengue fever; and 5 (13.2%) had dengue fever with hemorrhage. Four patients had epistaxis, and one woman had self-limited, abnormal vaginal bleeding of 24 hours’ duration.

Considering A. aegypti infestation rates and the large population of this area, (3 million in the Federal District and 8 million in the suburban areas) (7), the probability of an outbreak is high. Historically, the highest rates for A. aegypti in this area are reported in April and May (8). In 1997, 1,608,062 tourists arrived from countries that have dengue transmission (1,135,168 from neighboring countries, 358,286 from Paraguay) (9). Approximately 40% of these tourists arrived by plane. In 1998, >700,000 Argentineans left the country through Buenos Aires to travel to countries where dengue transmission occurs (7). Migration through bordering areas, especially in tropical regions of northern Argentina, is underreported.

The number of imported dengue cases in Buenos Aires and other cities in Argentina detected in the current period is substantially higher than the number detected in previous years. Argentina is at risk for an outbreak of dengue, and the health system of the country should be preparing for it.

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