Dengue in the United States, 1981

Duane J. Gubler, Ph.D.

Dengue Branch Division of Vector-Borne Viral Diseases

Center for Infectious Diseases

Introduction

Dengue, caused by a virus with four distinct serotypes, is usually a mild illness of short duration; classical symptoms include fever, vomiting, myalgia, headache, severe retro-orbital pain, and lower back pain. Infrequent complications include dengue hemorrhagic fever and dengue shock syndrome. There is no specific antiviral therapy for dengue, but for both classical dengue and dengue hemorrhagic fever, symptomatic and supportive measures are effective.

Dengue types 2 and 3 have been present in the Caribbean basin since at least the 1940s (1t); dengue type 1 was first recognized there during an outbreak in Jamaica in 1977, which was followed by numerous outbreaks in other countries of the region (2t). Dengue type 4 was recognized for the first time in the Western Hemisphere in 1981, when two U.S. travelers became ill after returning home from the island of St. Barthelemy, where, according to health authorities, an outbreak of dengue-like illness had been occurring for several months (3t).

Methods

Dengue surveillance in the United States is passive and, as such, depends upon suspected cases' being reported to CDC by various state health departments. Reporting is done on the CDC surveillance form, which is sent to the Centers with single or paired blood samples. Similarly, surveillance in Puerto Rico and the Caribbean region depends upon physicians' and health authorities' recognizing and reporting suspected cases and sending blood samples for testing. As a result, the number of suspected cases reported is considered to be an underestimate of the actual number of cases. Furthermore, paired serum samples are not received for many of the suspected cases, making serologic confirmation difficult. Cases specified in this report as confirmed have been documented as dengue either serologically or virologically. A new system of active surveillance is currently being instituted in Puerto Rico but was not in effect in 1981.

Results

In 1981, epidemic dengue occurred in the U.S. Virgin Islands and Puerto Rico (4t). Although the outbreak in the Virgin Islands was not studied thoroughly, serologic and virologic evidence suggested that both dengue 1 and dengue 4 were being transmitted. Most of the cases were reported from St. Thomas.

In Puerto Rico, reports of dengue-like illness began to increase in late July and peaked in October (Figure 1); analysis showed that the epidemic actually peaked in September (Figure 2). Although cases were reported from all over the island, most of the transmission occurred on the southwest coast. The early part of the epidemic was due almost exclusively to dengue type 1 (Figure 3). Dengue type 4 was introduced in September 1981, but confirmed cases remained sporadic through October. In November, transmission of this type began to increase, and by December, dengue 4 had replaced dengue 1 as the dominant serotype in Puerto Rico. In contrast to the dengue 1 epidemic in the summer, dengue 4 transmission occurred primarily in the San Juan metropolitan area. The clinical illness associated with both dengue 1 and dengue 4 infection in 1981 was primarily classic dengue fever, although sporadic cases with a variety of hemorrhagic manifestations occurred with both serotypes.

In the United States in the period 1977-1981, there were 943 imported cases of suspected dengue; 206 were confirmed as dengue infections. In August 1980, the first indigenous transmission of dengue fever in the United States since 1945 occurred in South Texas. In 1981, a total of 201 suspected cases were reported from 34 states; of these, only 98 had adequate specimens taken for testing; 44 were positive for dengue. Thirteen of the confirmed cases were reported from states where Aedes aegypti, the vector mosquito, is still present. New York, Florida, and Texas reported the largest numbers of cases. Most of the travelers with dengue had been to the Caribbean, but there were also patients with confirmed dengue who had traveled in Africa, India, Malaysia, and Honduras. The virus types involved were dengue 1 and 4.

Discussion

Since the vector, Ae. aegypti, is still widespread in the Gulf States and since increased frequency of air travel by humans increases the probability of the introduction of dengue virus into the United States, the potential for future epidemics of dengue in the southern United States remains high. During periods of increased risk of dengue virus introduction, active virologic surveillance is implemented in selected cities along the Gulf Coast.

References

1. Rosen L. Dengue type 3 infection in Panama. Am J Trop Med Hyg 1974;23:1205-6.

2. Pan American Health Organization (ed.). Dengue in the Caribbean, 1977. Proceedings of a workshop held in Montego Bay, Jamaica, 1978. PAHO Scientific Pub #375.

3. CDC. Dengue type 4 infections in U.S. travelers to the Caribbean. MMWR 1981;30:249-50.

4. CDC. Dengue fever in Puerto Rico--1981. MMWR 1982;31:103-4. Selected Bibliography CDC. Dengue--Cuba. MMWR 1981;30:317. CDC. Dengue type 2 virus in East Africa. MMWR 1982;31:407,8,13. CDC. Imported dengue type 4--Florida. MMWR 1982;30:622-3.

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