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Imported Dengue -- United States, 1996

Dengue is a mosquito-transmitted acute disease caused by any of four dengue virus serotypes (DEN-1, DEN-2, DEN-3, and DEN-4) and characterized by the sudden onset of fever, headache, myalgia, arthralgia, rash, nausea, and vomiting. This disease is endemic in most tropical areas of the world and has occurred in U.S. residents returning from travel to such areas. CDC maintains a laboratory-based passive surveillance system for imported dengue among U.S. residents. This report summarizes information about cases of imported dengue among U.S. residents for 1996, which indicated that most persons for whom travel history was known probably acquired infection in the Caribbean islands or Asia.

Serum samples from 179 persons who had suspected dengue with onset of symptoms in 1996 were submitted to CDC for diagnostic testing from 32 states and the District of Columbia. From these samples, 43 (24%) cases from 18 states and the District of Columbia were diagnosed serologically as dengue (single high titers of IgG in acute serum samples or by IgM detection in early convalescent samples) or by isolation of dengue virus. A diagnosis of dengue infection was negative in 102 (57%) patients and could not be determined in 34 (19%) patients because of unavailability of convalescent samples for serologic testing (1).

Of the 43 persons with laboratory-diagnosed dengue, sex was known in 39; 22 (56%) were male. Age was reported for 30 persons and ranged from 5 to 69 years (median: 33 years). The virus serotype (DEN-1 and DEN-2) was identified for five cases (Table_1). Travel histories, available for 37 persons, indicated that infections probably were acquired in the Caribbean islands (19 cases), Asia (11), Africa (three), the Pacific islands (two), Central America (one), and South America (one).

Clinical information was available for 28 patients with laboratory-diagnosed dengue. The most commonly reported symptoms were consistent with classic dengue fever (e.g., fever {93%}, headache {61%}, myalgia {57%}, rash {57%}, and arthralgia {18%}). Less frequently reported manifestations included diarrhea (five); eye pain (four); skin hemorrhages (two); and jaundice and depression (one each); low platelet counts (61,000-127,000/mm3, average 98,000/mm3 {normal: 150,000-450,000/mm3}) (eight); low white blood cell count (1900-3100/mm3, average 2550/mm3 {normal: 3200-9800/mm3}) (six); and elevated liver enzymes (one). At least two patients were hospitalized, and no deaths were reported.

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 transmitted by the mosquito Aedes aegypti, which is present in most tropical urban areas of the world. In the United States, the mosquito can be found during the summer in southeastern states, including parts of Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, and Texas. Dengue transmission in the United States is rare; however, autochthonous transmission of dengue was documented in Texas in 1980, 1986, and 1995 (2).

The incubation period of dengue is 4-7 days (range: 3-14 days). Most cases are characterized by mild manifestations, but infections in some persons can result in the more severe forms of the disease. Dengue hemorrhagic fever (DHF) is characterized by fever, low platelet count (less than or equal to 100,000/mm3), hemorrhagic manifestations, and evidence of increased vascular permeability (e.g., hemoconcentration {hematocrit increased by greater than or equal to 20% from baseline}, pleural or abdominal effusions, or hypoalbuminemia). Dengue shock syndrome (DSS) is DHF plus narrow pulse pressure (less than or equal to 20 mm Hg), hypotension, or shock (3). The fatality rate for patients with DSS can be as high as 44% (4).

During 1987-1993, the average annual number of laboratory-diagnosed cases reported to CDC was 20, but in 1994 the number increased to 38 (1). In 1995, an unusually high number (n=86) of imported laboratory-diagnosed cases of dengue was identified by CDC, reflecting the occurrence of outbreaks in Central American and Caribbean countries and the high number of cases detected by an active surveillance system in Texas (5,6). In 1996, the number of dengue and DHF cases reported to the Pan American Health Organization (n=276,758) was lower than the total for 1995 (n=316,187). Among persons in the United States with imported cases in 1996, five persons with history of travel to India reflect the DEN-2 epidemic that occurred in India (7). Among the imported infections acquired in the Caribbean islands during 1996, seven were diagnosed in persons from Maryland and Pennsylvania who traveled to the Caribbean during January (8).

The number of cases in this report represents a minimum estimate of the number of U.S. travelers with dengue. Because dengue is not a notifiable disease nationally or in most states, diagnostic samples may not be sent for testing or they may be sent to laboratories other than CDC; therefore, many imported cases may not be counted. To provide a better estimate of the total number of cases, state epidemiologists were asked to provide a listing of all dengue cases reported in their state with onset of illness in 1996. Nineteen states reported 51 cases; 22 (43%) cases had not been reported previously.

There is no vaccine for preventing dengue, and persons traveling to areas where dengue is endemic should avoid exposure to mosquito bites by using mosquito repellents and protective clothing and remaining in well screened or air conditioned areas. Ae. aegypti is an urban mosquito usually found in or near human dwellings. In domestic settings, the mosquito can be found resting in dark areas including closets, bathrooms, behind curtains, and under beds. The species bites usually during the early morning and late afternoon (9). The risk for exposure is higher in urban residential areas, but may be lower for tourists in some settings (e.g., beaches, hotels with well-kept grounds, and areas away from human habitation).

The incidence and geographic distribution of dengue have increased greatly in recent years, and health-care providers should consider dengue in the differential diagnosis of illness in all patients who have fever and a history of travel to tropical areas within 2 weeks of onset of symptoms. Because of the anticoagulant properties of acetylsalicylic acid (i.e., aspirin) and other nonsteroidal anti-inflammatory agents, only acetaminophen products are recommended for the management of pain and fever. For diagnosis, acute- and convalescent-phase serum samples should be obtained and sent through state or territorial health departments 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 (787) 766-5181; fax (787) 766-6596. Serum samples should be accompanied by a summary of clinical and epidemiologic information, including date of onset of disease, date of collection of sample, and a detailed recent travel history.


  1. Rigau-Perez JG, Gubler DJ, Vorndam AV, Clark GG. Dengue in travelers from the United States, 1986-1994. J Travel Med 1997;4:65-71.

  2. CDC. Dengue fever at the U.S.-Mexico border, 1995-1996. MMWR 1996;45:841-4.

  3. Pan American Health Organization. Guidelines for the prevention and control of dengue and dengue hemorrhagic fever in the Americas. Washington, DC: Pan American Health Organization, 1994.

  4. 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.

  5. CDC. Imported dengue -- United States, 1995. MMWR 1996;45:988-91.

  6. Pinheiro FP, Corber SJ. Global situation of dengue and dengue haemorrhagic fever, and its emergence in the Americas. World Health Stat 1997;50:161-9.

  7. World Health Organization. Dengue and dengue haemorrhagic fever, India. Wkly Epidemiol Rec 1996;71:335.

  8. Karp BE. Dengue fever: a risk to travelers. Maryland Medical Journal 1997;46:299-302.

  9. CDC. Biology and control of Aedes aegypti. Atlanta, Georgia: US Department of Health and Human Services, Public Health Service, CDC, 1979:7,13. (Vector topics no. 4).

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, 1996
                            ------------------------  Travel history, if known, of persons with
                                         Laboratory-        laboratory-diagnosed dengue
State                      Suspected      diagnosed            (serotype, if known)
Alabama                         4               0
Alaska                          1               0
Arkansas                        1               0
California                     10               0
Colorado                        8               2  India (DEN-2), Malaysia
District of Columbia            5               1  Ivory Coast
Florida                         5               1  Trinidad
Georgia                        11               1  Grenadine Islands
Hawaii                          6               2  Samoa (two cases)
Illinois                        6               0
Indiana                         1               0
Maine                           1               1  U.S. Virgin Islands (DEN-1)
Maryland                        9               6  U.S. Virgin Islands, British Virgin Islands
                                                    (five cases)
Massachusetts                  20               7  U.S. and British Virgin Islands and Puerto
                                                   Rico, U.S. Virgin Islands, Malaysia, India
                                                    (two cases)
Michigan                        3               0
Minnesota                       3               0
Montana                         1               0
Nebraska                        1               0
New Hampshire                   1               0
New Jersey                      3               1  India
New Mexico                      4               0
New York                       18               6  Jamaica, U.S. and British Virgin Islands,
                                                    Anguilla, India (DEN-2), Trinidad and
North Carolina                  4               2  India, Senegal
Ohio                            1               1  Philippines
Oregon                          8               1  Burma and Thailand
Pennsylvania                    7               3  Puerto Rico and British Virgin Islands, British
                                                    Virgin Islands (two cases)
Rhode Island                    3               3  (DEN-1, two cases)
South Carolina                  2               0
Texas                          23               2  Honduras, Nigeria
Vermont                         2               1  Barbados
Virginia                        1               0
Washington                      2               1  Southeast Asia
Wisconsin                       4               1  Ecuador

Total                         179              43

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