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Imported Dengue -- United States, 1993-1994

Dengue is a mosquito-transmitted acute disease caused by any of four virus serotypes (DEN-1, DEN-2, DEN-3, and DEN-4) and characterized by the sudden onset of fever, headache, myalgia, rash, nausea, and vomiting. The disease is endemic in most tropical areas of the world and has occurred in U.S. residents returning from travel to such areas. This report summarizes information about cases of imported dengue among U.S. residents during 1993 and 1994.

Serum samples from 148 U.S. residents who had suspected dengue with onset in 1993 (57 cases) and 1994 (91 cases) were submitted to CDC for diagnostic testing from 33 states Table_1. Of these, 46 (31%) cases from 17 states were serologically or virologically diagnosed as dengue (1) by isolation of dengue virus, detection of dengue-specific IgM, single high titers of IgG antibodies in acute serum samples, or a fourfold or greater rise in dengue-specific antibodies between acute- and convalescent-phase serum samples. Dengue serotype (DEN-2 and DEN-3) was identified for two cases.

Of the 46 persons with laboratory-diagnosed dengue, 25 (54%) were males. Age was reported for 32 and ranged from 1 year to 87 years (median: 27 years). Travel histories were available for 43 persons Table_1; infections probably were acquired in the Caribbean islands (21 cases), Mexico and Central America (10), and Asia (10). Two patients reported possible exposure in two locations: Australia and Asia, and Asia and Africa.

Clinical information was available for 40 of 46 laboratory-confirmed cases. The most commonly reported symptoms were consistent with classic dengue fever (e.g., fever {92%}, myalgia {48%}, rash {48%}, and headache {42%}). Other manifestations included petechiae or purpura (four patients); low white blood cell count (1000- 2700/mm3 {normal: 3200-9800/mm3}) (13 patients); low platelet count (20,000-134,000/mm3 {normal: 150,000-450,000/mm3}) patients).

Six patients were hospitalized. One patient (aged 12 years) with secondary dengue infection developed fever, thrombocytopenia, epistaxis, right pleural effusion, ascites, and hypotension -- signs compatible with dengue shock syndrome (DSS). One patient (aged 11 years), who also had a secondary infection, developed mild disseminated intravascular coagulation. One patient (aged 49 years) with an unspecified serologic response had fever, myalgias, thrombocytopenia, leukopenia, elevated liver function test results, and hypotension (blood pressure 90/48 mmHg). Reported by: State and territorial health depts. Dengue Br, Div of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Dengue is not endemic in the United States. However, because the incubation period is 3-14 days, U.S. residents who become infected during travel to tropical areas may have onset of illness after returning to the United States (2). Although most dengue infections are associated with mild illness, the risk for dengue hemorrhagic fever (DHF) is greater in some persons -- particularly those with repeat (secondary) infection. DHF is characterized by fever, platelet count less than or equal to 100,000/mm3, hemorrhagic manifestations, and leaky capillary syndrome (hemoconcentration, hypoalbuminemia, or pleural or abdominal effusions). DSS includes DHF and hypotension or narrow pulse pressure (less than or equal to 20 mmHg) (3,4) and is associated with a high fatality rate (5).

The incidence of DHF is increasing in the Americas: since 1982, dengue epidemics with associated DHF have occurred in Aruba, Brazil, Colombia, Curacao, Dominican Republic, El Salvador, French Guiana, Honduras, Mexico, Nicaragua, Puerto Rico, St. Lucia, Suriname, and Venezuela. In addition, dengue is endemic in many islands in the Caribbean, in Mexico, and in most countries in Central and South America (6). In 1994, outbreaks of dengue were reported from Brazil, Costa Rica, Dominican Republic, Haiti, Mexico, Nicaragua, Panama, Puerto Rico, and Venezuela. Nicaragua and Panama recently confirmed infections attributable to DEN-3 (7), a serotype that was last isolated in the Americas in 1977 (8).

In the Americas, dengue is transmitted by Aedes aegypti mosquitoes. Although nearly eradicated from the region during the 1960s, this species is now present in most tropical areas of the Americas. In the United States, A. aegypti is present year-round in the southernmost Gulf of Mexico coast states from Texas to Florida; a small focus also exists on the island of Molokai in Hawaii. Autochthonous transmission of dengue has not occurred in the United States since 1986 (6); however, introduction of the virus by persons who have acquired infections in other countries could result in local transmission.

The 37 laboratory-confirmed cases identified in 1994 represent almost twice the average number of similar cases identified annually during 1987-1993 (n=20) and the highest number of positives identified since 1982 (n=45) (6). However, these totals do not include cases that may have been reported to state health departments but for which specimens were not submitted for testing at CDC. In addition, in 1994, the California Department of Health Services received reports of five cases of suspected dengue that were documented at the state's Viral and Rickettsial Disease Laboratory (9).

Compared with previous years, a higher proportion of cases reported in 1994 were characterized by severe disease. The three persons with life-threatening illness underscore the importance of early recognition and treatment of the severe manifestations of dengue infection.

The prevention of dengue infection in tropical locations requires avoiding exposure to mosquitoes (10) and includes the continuous use of mosquito repellent and protective clothing. Although the Aedes species that transmits dengue may bite at any time during the day, peak activity occurs during the early morning and late afternoon. Ae. aegypti usually is present in peridomestic settings and is found most often in dark areas such as closets and bathrooms, behind curtains, and under beds. For tourists, the risk for exposure to dengue may be lower in some settings, including beaches, hotels with well-kept grounds, and heavily forested areas and jungles.

Health-care providers should consider dengue in the differential diagnosis for all patients who have compatible manifestations and a recent history of travel to tropical areas. When dengue is suspected, patients should be monitored for evidence of hypotension, hemoconcentration, and thrombocytopenia. Because of the anticoagulant properties of acetylsalicylic acid (i.e., aspirin), only acetaminophen products are recommended for management of fever. Acute- and convalescent-phase serum samples should be obtained for viral isolation and serodiagnosis and sent for confirmation through state or territorial health department to CDC's Dengue Branch, Division of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, 2 Calle Casia, San Juan, PR 00921-3200; telephone (809) 766-5181; fax (809) 766-6596. Serum specimens should be accompanied by a summary of clinical and epidemiologic information, including a detailed travel history with dates and location of travel and dates of onset of illness and blood collection.


  1. CDC. Case definitions for public health surveillance. MMWR 1990;39(no. RR-13):10-1.

  2. Benenson AS, ed. Control of communicable diseases in man. 15th ed. Washington, DC: American Public Health Association, 1990:119.

  3. Morens DM. Antibody-dependent enhancement of infection and the pathogenesis of viral disease. Clin Infect Dis 1994;19:500-12.

  4. Pan American Health Organization. Dengue and dengue hemorrhagic fever: guidelines for prevention and control. Washington, DC: Pan American Health Organization, 1994:12-3.

  5. Tassniyom S, Vasanawathana S, Chirawatkul A, Rojanasuphot S. Failure of high-dose methylprednisolone in established dengue shock syndrome: a placebo-controlled, double-blind study. Pediatrics 1993;92:111-5.

  6. Rigau-Perez JG, Gubler DJ, Vorndam AV, Clark GG. Dengue surveillance -- United States, 1986-1992. In: CDC surveillance summaries, MMWR 1994;43(no. SS-2):7-19.

  7. CDC. Dengue type 3 infection -- Nicaragua and Panama, October-November 1994.

  8. Gubler DJ. Dengue and dengue hemorrhagic fever in the Americas. Puerto Rico Health Sciences Journal 1987;6:107-11.

  9. Division of Communicable Disease Control. Dengue and dengue hemorrhagic fever -- a significant risk for travelers. California Morbidity, January 13, 1995.

  10. CDC. Advisory memorandum no. 109 -- dengue update. Atlanta: US Department of Health and Human Services, Public Health Service, March 10, 1995.

Note: To print large tables and graphs users may have to change their printer settings to landscape and use a small font size.

TABLE 1. Suspected and laboratory-diagnosed cases of imported dengue, by state
-- United States, 1993-1994
                          Cases           Travel history, if known,
                 ----------------------   of persons with laboratory-
                            Laboratory-   diagnosed dengue
State            Suspected   diagnosed    (serotype, if known)
Alabama                1           0
Arizona                3           1       Puerto Rico
California             5           1       India
Colorado               3           2       Mexico, Nicaragua
  of Columbia
                       4           2       Sri Lanka, Mexico
Florida               12           3       Costa Rica, Puerto Rico, Bali
Georgia                5           1       Puerto Rico, French West Indies
Hawaii                 4           0
Illinois               3           2       Dominican Republic,
Iowa                   3           0
Kansas                 1           0
Louisiana              2           0
Maine                  1           0
Maryland               4           0
Massachusetts         22           9       Philippines and Thailand, Haiti,
                                           Bangladesh, four from Puerto
Minnesota              4           3       Somalia, Kenya, Cambodia;
                                             Thailand; Mexico
Mississippi            5           0
Montana                1           0
New York              24          12       Philippines, Thailand, Myanmar
                                             Dominican Republic, Grenada,
                                             two from Jamaica, five from Puerto Rico
North Carolina         6           1       Philippines and India
North Dakota           1           1       Puerto Rico and Dominican Republic
Ohio                   5           4       Australia and Southeast Asia (DEN-3),
                                             El Salvador, two from British Virgin
Oklahoma               2           0
Oregon                 4           0
Pennsylvania           3           0
South Carolina         1           0
Tennessee              2           0
Texas                  3           1       Honduras
Utah                   1           1       Mexico (DEN-2)
Vermont                1           0
Virginia               3           1
Washington             6           1      Belize
Wisconsin              3           0

Total                148          46

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