Dengue Virus Infections Among Travelers Returning from Haiti --- Georgia and Nebraska, October 2010

In October 2010, a Nebraska clinician notified the state's Central District Health Department (CDHD) of a cluster of dengue-like illnesses in six of 28 missionary workers from Nebraska and Georgia who recently had returned after 7--11 days in Haiti. Infection with the mosquito-transmitted dengue virus (DENV) later was confirmed by laboratory testing in seven persons, five of whom were hospitalized. CDHD, the Nebraska Department of Health and Human Services (NDHHS), the Georgia Department of Public Health (GDPH), and CDC conducted a retrospective cohort study to assess the pretravel dengue knowledge and mosquito-avoidance practices of those with and without laboratory-confirmed infection. This report describes the results of that study, which indicated that 90% of those in the study had a pretravel health-care appointment, 57% sought travel advice on the Internet, and 24% used mosquito repellent several times a day; neither pretravel knowledge nor mosquito-avoidance practices were significantly associated with absence of DENV infection. Clinicians should be vigilant for dengue among travelers returning from Haiti and other areas where DENV is endemic or likely to be endemic and should report suspected cases of dengue to public health authorities (1).

On October 18, 2010, CDHD notified NDHHS of six persons who experienced fever, headache, arthralgia, and myalgia upon returning from a 7--11 day missionary trip to Haiti's Carrefour community. Initial interviews indicated that these persons traveled with a larger missionary group of 28 persons (22 from Nebraska and six from Georgia). NDHHS, CDHD, GDPH, and CDC collaborated to collect serum specimens for dengue testing and to administer a survey to assess travelers' dengue knowledge and mosquito-avoidance practices.

Specimens were collected from 21 Nebraska travelers and two Georgia travelers. Specimens were sent to CDC for diagnostic testing along with dengue case investigation forms (DCIFs)* that included demographic, epidemiologic, and clinical information.

Because a substantial portion of DENV infections can be asymptomatic (2), both symptomatic travelers and travelers who were not ill underwent laboratory testing for DENV infection. Specimens collected from symptomatic travelers included an acute specimen (collected ≤5 days after symptom onset from travelers reporting any symptoms during travel or within 14 days of return home) and a convalescent specimen (collected >5 days after symptom onset). Specimens collected from travelers who were not ill included a first specimen (collected ≤8 days of return home) and a second specimen (collected ≥14 days after the first specimen). Acute and first specimens were tested for the presence of DENV nucleic acid by reverse transcription--polymerase chain reaction (RT-PCR) using primers specific for DENV-1, DENV-2, DENV-3, and DENV-4 (3). Acute and first serum specimens with a negative RT-PCR result also were tested by anti-DENV immunoglobulin M antibody capture enzyme-linked immunosorbent assay (MAC-ELISA). All travelers who had a negative RT-PCR result from the acute or first specimen were asked to provide a convalescent or second specimen for testing by MAC-ELISA. A case was defined as DENV infection confirmed by positive RT-PCR or MAC-ELISA. Noncases were laboratory-test--negative (i.e., RT-PCR was negative or not performed, and MAC-ELISA was negative in the convalescent or second specimen). A negative MAC-ELISA and RT-PCR in the sole acute or first specimen with no convalescent or second specimen provided was considered indeterminate.

Eighteen travelers submitted specimens that were tested by RT-PCR; DENV-1 was detected in specimens submitted by seven of these travelers. Specimens from 11 travelers that tested negative by RT-PCR also tested negative by MAC-ELISA. Of these 11, nine subsequently submitted a convalescent or second specimen, all of which tested negative by MAC-ELISA. Two of the 11 travelers had indeterminate test results. Five travelers provided only a convalescent specimen; all tested negative by MAC-ELISA. Thus, of the 28 travelers in this group, 21 (75%) had complete DENV laboratory testing, seven of whom (33%) were infected with DENV-1.

All 28 travelers were asked to participate in a survey using a 53-item questionnaire to collect information regarding demographics, medical and travel history, pretravel preparations and knowledge, mosquito-avoidance practices while in Haiti, and illnesses during and after travel. Twenty-five (89%) travelers participated: 21 by telephone or in-person interviews, two by proxy, and two by self-administration.

The group had traveled to Haiti for 7--11 days, during which they offered spiritual and community support and educational activities. Although pretravel medical preparation was left up to each person, travel organizers referred them to a CDC Internet site for travelers' health recommendations. While in Haiti, the group stayed together in a house lacking functional window and door screens, air-conditioning, and electricity. The majority of activities were conducted within walking distance of the house during daylight hours; evening group meetings were held nearby on a building rooftop.

Twenty-one (75%) of the 28 travelers completed both questionnaires and laboratory testing and were included in the analysis. Of these, 12 (57%) were male. Median age was 34 years (range: 16--69 years), and all were non-Hispanic whites. Six (29%) had lived and 14 (67%) had traveled outside of the continental United States previously; none reported previous travel to Haiti or previous DENV infection.

Based on information collected on DCIFs and questionnaires, 16 (76%) of the 21 travelers included in the analysis reported one or more signs or symptoms of illness during travel or within 14 days of returning home; 12 (75%) reported febrile illness, and 10 (63%), including all seven confirmed cases, reported illnesses compatible with 2009 World Health Organization (WHO) clinical criteria for probable dengue (4). Among the seven persons with DENV infection, all had illness onset 3--7 days (median: 4 days) after returning home (Figure), sought medical care, and recovered. Five (71%) of the seven were hospitalized for 3--5 days (median: 3 days) within 3--6 days (median: 5 days) of onset. Of these, four had hemorrhagic manifestations, including two with petechiae, one with purpura, and one with petechiae and menorrhagia. Review of hospital discharge summaries showed that none of those hospitalized met the WHO clinical criteria for severe dengue (4).

Nineteen (90%) of the 21 travelers included in the analysis reported having a pretravel health-care appointment, and 12 (57%) reported seeking pretravel health advice on the Internet. Twenty (95%) reported having pretravel knowledge about infectious disease risks in Haiti, and 10 (48%) reported pretravel knowledge about dengue. Ten (48%) travelers recalled having been bitten by a mosquito during the trip, and five (24%) reported using insect repellent multiple times a day. Ten (48%) had worn long pants, and two (10%) had worn long-sleeved shirts more than 1 day while in Haiti. When questionnaire responses from persons with DENV infection were compared with those from persons without DENV infection, no statistically significant association was found between having DENV infection and pretravel knowledge or mosquito-avoidance practices (Table).

Reported by

Teresa Anderson, Jeremy Collinson, Trina Vap, Central District Health Dept, Grand Island; Robin M. Williams, Nebraska Dept of Health and Human Svcs and Univ of Nebraska-Lincoln; Thomas J. Safranek, MD, Dennis P. Leschinsky, Annette K. Bredthauer, DVM, Nebraska Dept of Health and Human Svcs.Julie Gabel, DVM, Div of Public Health, Georgia Dept of Public Health. Bryan F. Buss, DVM, Career Epidemiology Field Officer Program, Office for Public Health Preparedness and Emergency Response; Mark J. Sotir, PhD, Emily S. Jentes, PhD, Div of Global Migration and Quarantine; Jorge L. Muñoz-Jordan, PhD, Elizabeth A. Hunsperger, PhD, D. Fermin Argüello, MD, Div of Vector-Borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases; Parvathy Pillai, MD, Tyler M. Sharp, PhD, EIS officers, CDC. Corresponding contributor: Tyler M. Sharp, tsharp@cdc.gov, 787-706-2399.

Editorial Note

This report confirms recent DENV transmission in Haiti with an attack rate of ≥25% among a group of travelers who were in the country for 7--11 days. A similar investigation of dengue among short-term travelers to the Dominican Republic in 2008 indicated an attack rate of ≥42%, with laboratory testing limited to those with a clinical presentation consistent with dengue (5). Little is known about the epidemiology of dengue in Haiti. However, this report corroborates previous findings of dengue among military personnel deployed to Haiti (6) and high DENV seroprevalence among Haitian children (7), indicating that DENV likely is endemic in Haiti.

In this report, although nearly all travelers sought pretravel health-care advice, only 48% had pretravel knowledge about dengue, 48% wore long pants on more than 1 day, and 24% used mosquito repellent multiple times a day. Travelers should be aware of the health risks associated with their travel and seek a pretravel medical consultation, in which they should receive destination-specific health advice. To inform persons traveling to DENV-endemic areas, clinicians and travel organizers should consult travel medicine resources, including travelers' health Internet sites,† to provide information to travelers about DENV transmission, symptoms of dengue, and mosquito-avoidance practices, including use of insect repellent, protective clothing, and insecticides.

Only 29% of those with DENV infection in this report recalled mosquito bites; travelers to DENV-endemic areas should adhere to mosquito-avoidance strategies even if mosquitoes are not apparent. Because Aedes aegypti, the primary mosquito vector for DENV, typically lives inside or close to human dwellings and has peak biting periods during daylight hours (8), travelers should be advised to use protective measures both indoors and outdoors, particularly during the daytime.

Clinicians should be vigilant to recognizing dengue among returning travelers. In this cluster, a clinician identified dengue-like illness among travelers returning from Haiti, submitted specimens for testing, and promptly notified public health authorities. Although clinical management should not be delayed pending diagnostic testing, laboratory testing is required to confirm diagnoses of dengue. Furthermore, previous DENV infection is considered a risk factor for increased severity of disease upon subsequent infection with DENV of a differing serotype (4); therefore, laboratory testing can allow clinicians to inform travelers of increased risk for severe dengue if they are infected again upon subsequent travel to DENV-endemic areas.

Prompt reporting of suspected cases of dengue to public health authorities can facilitate diagnostic testing and prevent secondary DENV transmission. Recent reports of DENV transmission in Hawaii and Florida (9,10) indicate the existence of competent mosquito vectors in certain areas of the United States. As such, the potential exists for domestic transmission of DENV imported by viremic travelers returning to areas in the United States with competent vectors. Early detection of cases and a rapid public health response might prevent such importations from leading to outbreaks.

All travelers to Haiti should seek pretravel health counseling, preferably 4--6 weeks before travel, receive information about risks for DENV infection, and employ recommended mosquito-avoidance practices. Clinicians evaluating travelers with febrile illness who recently have returned from Haiti or other DENV-endemic areas are encouraged to consider dengue in their differential diagnosis, submit specimens for laboratory testing, and report cases of dengue expeditiously to local or state health departments (Box).

Acknowledgments

Mike Darbro, Central District Health Dept, Grand Island; Brian Buhlke, DO, Lone Tree Medical Associates PC, Central City; Cindy Ference, Loup Basin Public Health Dept, Burwell; Alison Keyser-Metobo, MPH, Dorothy Smiley, Nebraska Dept of Health and Human Svcs. Emily Zielinski-Gutierrez, PhD, Erin J. Staples, MD, Carmen L. Perez-Guerra, PhD, Kay Tomashek, MD, Harold Margolis, MD, Div of Vector-Borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases; Julie Magri, MD, Betsy L. Cadwell, MSPH, Scientific Education and Professional Development Program Office, CDC.

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