Dengue activity in Puerto Rico has increased substantially since August of 1986 (Figure 2). Of the 5,564 cases of suspected dengue reported in the first 10 months of the year, 4,640 (83%) occurred from August through October. Seven hundred and forty cases have been virologically or serologically confirmed in 1986 (Table 3), compared with six cases in 1983, 11 cases in 1984, and 133 cases in 1985. The male to female ratio of confirmed cases for 1986 was 1:1, with all ages affected. Cases have been confirmed in 64 of the 78 Puerto Rican municipalities (82%).

Two hundred and eleven dengue viruses have been isolated in 1986, 152 (72%) during August, September, and October. Three dengue serotypes (DEN-1, DEN-2, and DEN-4) have been co-circulating in Puerto Rico since late 1985. In 1986, DEN-1 and DEN-4 have been the predominant serotypes island-wide (45% and 44% respectively), followed by DEN-2 (11%). Since August, however, most transmission has occurred in the San Juan metropolitan area (63% of confirmed cases), and DEN-4 has been the predominant serotype with 75 (49%) isolates, followed by DEN-1 with 58 isolates (38%) and DEN-2 with 19 isolates (13%).

Although the majority of cases have presented as classical dengue fever, 26% of patients with 356 laboratory-confirmed disease have reported at least one hemorrhagic manifestation. The most common of these have been petechiae, purpura/ecchymosis, bleeding of gums, hematuria, and thrombocytopenia. Moreover, hospitalization has increased, with 100 patients (14% of total) with confirmed dengue infection hospitalized. This is a hospitalization rate of 135/1,000 patients with confirmed dengue infection in 1986, compared with 75/1,000 in 1985 and 19/1,000 in 1982 during the last outbreak of DEN-4. As the hospitalization data suggest, there has been an increase in severe hemorrhagic disease associated with the outbreak. The rate of confirmed dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) per 1,000 persons with confirmed dengue infection was 14 in 1986, compared with 8/1,000 in 1985. Although the rates are still low, they represent a significant increase over previous years when epidemics were larger and there were no cases of DHF/DSS. Also, Puerto Rico has experienced its first virologically confirmed fatal case of DHF/DSS. To date in 1986, 12 cases of severe hemorrhagic disease have been confirmed virologically and/or serologically as dengue. Ten of these cases meet WHO clinical criteria for DHF/DSS; two patients did not have hemoconcentration but had severe upper gastrointestinal hemorrhage and thrombocytopenia.

The ten cases that meet WHO clinical criteria for DHF/DSS included six children (five infants less than 1 year of age) and four adults. The ratio of males to females was 1:1. There were four patients with dengue shock syndrome (three infants and one adult); two confirmed cases were fatal (one in a 30-year-old female and the other in a 6-month-old male). DEN-4 was isolated from the former, and DEN-2, from the latter. The most common hemorrhagic manifestations observed in patients with confirmed DHF/DSS were petechiae (five patients), hematemesis (five patients), and hematuria (three patients). In addition to the five patients above who had hematemesis, two other patients (one adult and one child) had severe upper gastrointestinal bleeding and thrombocytopenia in the absence of hemoconcentration.

Measures taken to control the outbreak include increased public education on eliminating mosquito larval habitats, initiating education programs in the public school system on environmental sanitation, and widespread application of insecticide with truck-mounted equipment. An emergency hospitalization plan has been developed, but has not yet been fully implemented. Reported by Puerto Rico Dept of Health; Dengue Br, Div of Vector-Borne Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The recent severe illnesses in Puerto Rico are clinically compatible with DHF/DSS in southeast Asia (1). Eleven confirmed cases since September 1985, have met WHO criteria for DHF/DSS with hemoconcentration and evidence of plasma leakage. Two other patients had severe upper gastrointestinal bleeding similar to that observed in Indonesia (2). Seven of the confirmed cases were in children--five of these were infants. In previous Puerto Rican epidemics, most severe disease was in adults (3).

Puerto Rico experienced its first reported dengue outbreak in 1915 (4). Subsequent outbreaks occurred in 1945, 1963, 1969, 1976, 1977, 1978, 1981, and 1982 (Dengue Branch, Division of Vector-Borne Viral Diseases, Center for Infectious Diseases, CDC, unpublished data). Laboratory-based surveillance for DHF/DSS began in 1975. From that time through 1985, 47,196 suspected cases of dengue were reported to the San Juan Laboratories. During the same time period, 19% of cases for which there were adequate laboratory specimens (8,816) were confirmed as dengue; and 230 (3%) of persons with confirmed cases were hospitalized. During 1986, 14% of the 5,564 persons with confirmed dengue infection have been hospitalized, and there have been 10 cases of confirmed DHF/DSS. Thus, both the reporting of severe dengue disease and the number of persons hospitalized with severe dengue disease have increased during 1986.

Some of the present increase in the number of reported dengue cases may relate to improved awareness. When The first fatal case of DHF/DSS in Puerto Rico occurred in August, it was followed by numerous press releases, and clean-up campaigns were initiated. In general, the awareness of dengue in both lay and medical communities has increased. The monthly proportion of patients hospitalized with confirmed cases, however, remained stable, even after the fatality was announced. Moreover, the confirmation rate for dengue began to increase in June (weeks 24 through 25 of the outbreak), 2 months before the response to the press campaign.

Because the 1978 and 1981 dengue outbreaks in Puerto Rico were caused by DEN-1 and the 1982 outbreak was caused by DEN-4, it was considered unlikely that the present outbreak would be very large. DEN-2 is also being transmitted in Puerto Rico, and recent virus isolation data suggest that transmission of this serotype may be increasing. Since the last major epidemic of DEN-2 was in 1976-1977, a large number of individuals in Puerto Rico (mainly children) are susceptible to this virus. Furthermore, studies by CDC on school children in Puerto Rico have shown that by the first grade, 30% to 50% of school children have serologic evidence of a past dengue infection.

Evidence from Thailand and Cuba suggests that secondary DEN-2 infection following DEN-1 infection at a 3- to 5-year interval may be a risk factor for epidemic DHF/DSS. If this is true, Puerto Rico is at increased risk for an epidemic of DHF/DSS. Moreover, with the co-circulation of multiple serotypes, the epidemiologic situation in Puerto Rico is now very similar to that in many southeast Asian countries where DHF/DSS is endemic.

Currently, a major effort is being made to control the vector mosquito, Aedes aegypti. The integrated approach being used includes community-based source reduction, insecticide application, and health education.

Risk of dengue infection for travelers to endemic areas appears to be small. However, travelers to and residents of endemic areas should take precaution to avoid mosquito bites and to remain in well-screened areas when possible. Outdoors, exposures to mosquitoes can be reduced by wearing clothing that adequately covers the arms and legs and by applying mosquito repellent.

References

1. World Health Organization. Guide for diagnosis, treatment and control of dengue hemorrhagic fever. 2nd ed. Geneva, Switzerland: Technical Advisory Committee on Dengue Hemorrhagic Fever for the Southeast Asian and Western Pacific Regions, World Health Organization, 1980.

2. Sumarmo, Wulur H, Jahja E, Gubler DJ, Suharyono W, Sorensen K. Clinical observations on virologically confirmed fatal dengue infections in Jakarta, Indonesia. Bull WHO 1983;61:693-701.

3. Woodall JP, Lopez-Correa RH, Sather GE, Moore CG. The absence of epidemic dengue hemorrhagic fever from the Americas. In: Hotta S, ed. Proceedings of the First ICMR Seminar. Kobe, Japan: International Center for Medical Research, 1981:95-106.

4. King WW. The epidemic of dengue in Porto Rico (sic), 1915. New Orleans Med Surg J 1917;69:564-71.

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