Outbreak of Influenza A Infection Among Travelers -- Alaska and the Yukon Territory, May-June 1999

On June 18, 1999, CDC and Health Canada received reports from public health authorities in Alaska and the Yukon Territory about clusters of febrile respiratory illness and associated pneumonia among travelers and tourism workers. This report presents information about the outbreak. Laboratory evidence, including rapid influenza A antigen-detection tests and viral cultures from respiratory specimens, has implicated influenza A virus as the cause of illness.

As of June 29, CDC has received reports of 428 cases of acute respiratory infection (ARI) among tourists who traveled to Alaska and the Yukon Territory from May 22 through June 28 on seven separate week-long cruises. For 187 (48%) of the 386 ill persons whose dates of illness onset were known, illness occurred before or within 48 hours after boarding a cruise ship, suggesting that transmission occurred during a preceding land-based tour. The ARI incidence for the 386 cases was 3.8% among 10,110 passengers for a 7-day travel itinerary; the ARI attack rate was 5.5 per 1000 passenger-days. One hundred thirty-two (34%) cases met criteria for influenza-like illness (ILI) (i.e., fever or feverishness with cough or sore throat); four persons were hospitalized for pneumonia. No deaths have been reported. Among tourism workers, 104 cases of ARI have been reported.

Reported by: Div of Public Health, Section of Epidemiology, and Section of Laboratories, Alaska Dept of Health and Social Svcs. Travel Medicine, Laboratory Center for Disease Control, Health Canada. Arctic Investigations Program, Influenza Br, Div of Viral and Rickettsial Diseases, and Surveillance and Epidemiology Br, Div of Quarantine, National Center for Infectious Diseases, CDC.

Editorial Note:

Summer outbreaks of influenza A have been reported previously among tourists in the United States and Canada (1-3). In 1998, approximately 40,000 tourists and tourism workers were affected by an influenza outbreak in Alaska and the Yukon Territory (4). As with the 1998 summer outbreak of influenza A in this region, the findings in this report suggest that influenza appears to be initially transmitted during land-based travel among tourists on combination land and sea tours and among tourism workers.

In anticipation of possible persistent influenza activity, some cruise lines initiated policies to vaccinate crew members during the fall of 1998 to decrease the risk for influenza transmission by crew members to travelers. In addition, health departments in Alaska, the Yukon Territory, and British Columbia and collaborating cruise lines have implemented summertime respiratory illness surveillance.

In response to this outbreak, CDC and Health Canada developed recommendations for travelers to the region and for regional tourism workers. These recommendations are based on the following assumptions and considerations: 1) persons who travel with large organized groups are at risk for exposure to influenza, 2) new cases of influenza A infection probably will continue to occur among tourists to the region, 3) persons aged greater than or equal to 65 years and persons with underlying health conditions are at increased risk for influenza-related complications, 4) tourism workers have frequent contact with persons at risk for influenza-related complications, 5) influenza vaccine availability during the summer is limited, and 6) when the supply of influenza vaccine is inadequate, influenza A-specific antiviral medications (i.e., amantadine or rimantadine) have a primary role in influenza A prevention and treatment.

On the basis of these considerations, CDC and Health Canada recommend that persons aged greater than or equal to 65 years or who have certain underlying chronic medical conditions (e.g., pulmonary or cardiac disease) should consult their health-care providers before traveling to Alaska and the Yukon Territory this summer, regardless of their vaccination status, about their risk for influenza, the symptoms of influenza, and the advisability of carrying antiviral medications for either prophylaxis or treatment for influenza A infections. These groups are at increased risk for serious complications from influenza, including pneumonia, hospitalization, and death (5). Both amantadine and rimantadine can reduce the duration of influenza A illness and viral shedding if administered within 48 hours of symptom onset; however, these drugs also may cause side effects (particularly central nervous system or gastrointestinal effects) and may require dosage adjustment in elderly patients and those with underlying renal or hepatic disease. Health-care providers in Alaska, the Yukon Territory, and British Columbia and on cruise ships in regional waters who may be providing care for persons with ILI should consider prescribing antiviral agents for patients with febrile respiratory illness. Rapid antigen-detection tests for influenza, if available, will be useful for early diagnosis. CDC, in collaboration with state and provincial health authorities and the tourism industry, is working to implement surveillance for ILI among travelers and tourism workers for the remainder of the Alaska/Yukon Territory tourist season.

In the United States and Canada, health-care providers evaluating patients with febrile respiratory illnesses or pneumonia should obtain a travel history and consider influenza A in their differential diagnosis. Additional information about this outbreak is available on the CDC World-Wide Web sites, http://www.cdc.gov/travel/index.htm and http://www.cdc.gov/ncidod/diseases/flu/fluvirus.htm.

References

1. CDC. Outbreak of influenza-like illness in a tour group--Alaska. MMWR 1987;36:697-8,704.
2. CDC. Update: outbreak of influenza A infection--Alaska and the Yukon Territory, July- August 1998. MMWR 1998;47:685-8.
3. Health Canada. Influenza A outbreak on a cruiseship. Can Comm Dis Rep 1998;24:9-11.
4. Zane S, Uyeki T, Bodnar U, et al. Influenza in travelers, tourism workers, and residents in Alaska and the Yukon Territory, summer 1998 [Poster]. Presented at the 6th Conference of the International Society for Travel Medicine, Montreal, Canada, June 6-10, 1999.
5. CDC. Prevention and control of influenza--recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 1999;48(no. RR-4).

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