No Evidence of Avian Influenza A (H5N1) Among Returning US Travelers

Justin R. Ortiz; Teresa R. Wallis; Mark A. Katz; LaShondra S. Berman; Amanda Balish; Stephen E. Lindstrom; Vic Veguilla; Kathryn S. Teates; Jacqueline M. Katz; Alexander Klimov; and Timothy M. Uyeki


Emerging Infectious Diseases. 2007;13(2):294-297. 

In This Article

The Study

We retrospectively analyzed available data on US patients with suspected H5N1 virus infection that were reported to CDC by clinicians and public health departments from February 2003 through May 2006. Clinical and epidemiologic data about reported patients were communicated to CDC by telephone, email, and/or fax. For each patient, we assessed whether criteria for recommended H5N1 testing were met (suspected H5N1 case definition). The suspected H5N1 case definition had 2 components: the hospitalized case definition included severe respiratory illness and recent travel to an H5N1-affected country; and the ambulatory case definition included acute respiratory illness, contact with domestic poultry or a known or suspected H5N1 case-patient, and recent travel to an H5N1-affected country[6] (Figure 1). Contact was defined as proximity ≤1 m, and direct contact was defined as physical touching.

Influenza testing of suspected US cases of avian influenza A (H5N1) reported to the Centers for Disease Control and Prevention (CDC) from February 2003 through May 2006. *Of the 37 samples tested by CDC, 35 were respiratory samples, 1 was serum, and 1 was a lung specimen. All 35 respiratory samples received by CDC were tested for human influenza by reverse transcription-PCR, and the serum sample was tested by microneutralization assay. †CDC suspected H5N1 case definition, February 2, 2004-June 7, 2006[6]: a patient is hospitalized and has radiographically confirmed pneumonia, acute respiratory distress syndrome, or other severe respiratory illness for which an alternate diagnosis has not been established; and the patient has a history of travel within 10 days of symptom onset to a country with documented H5N1 avian influenza in poultry and/or humans; or a patient is hospitalized or ambulatory and has a documented temperature >38°C (>100.4°F); and has a cough, sore throat, or shortness of breath; and has a history of contact with domestic poultry or a patient with known or suspected H5N1 case in an H5N1-affected country <10 days of symptom onset. BOOP = bronchiolitis and obliterans organizing pneumonia; TSS = toxic shock syndrome.

If a patient met the suspected H5N1 case definition, or if exposure data were incomplete and clinicians or public health authorities had persistent concerns, H5N1-specific testing was recommended by CDC. A standard case report form was completed by state health departments.

Diagnostic testing for patients with suspected H5N1 virus infection was performed at CDC, state laboratories, or both. Procedures for reverse transcription-PCR (RT-PCR) and microneutralization assay for H5N1 have been previously described.[7,8] Epidemiologic and laboratory data were analyzed by using EpiInfo version 3.3.2 (CDC, Atlanta, GA, USA).

Fifty-nine patients from 26 states were reported to CDC for suspicion of H5N1 virus infection from February 2003 through May 2006 (Table and Figure). Nineteen (37%) were male (n = 52), and the median age was 47 years (n = 49, range 2-87 years). Of the samples received from 37 patients that were tested at CDC, none had evidence of H5N1 virus infection. CDC tested samples from 8 patients for human influenza A only, and 5 were positive. Among the samples from 22 (37%) patients not tested at CDC, 4 (7%) were tested for H5N1 at state public health laboratories, and all were negative. Of the remaining 18 (31%) patients, 15 were not tested for H5N1 and state testing data were unavailable for 3 (Figure 1).

On the basis of available information, 27 (46%) patients met the CDC suspected H5N1 case definition ( Table 1 ). Fourteen (24%) had severe, acute respiratory illness with recent travel to an H5N1-affected country. Overall, 25 (42%) patients, including 2 of 4 who died, tested positive for human influenza A virus infection. In addition, 52% of the 27 patients who met the CDC suspected H5N1 case definition had samples that tested positive for human influenza A. Four influenza A cases occurred outside the US influenza season. Of the influenza A-positive patients, 10 had H3N2 viral isolates that were characterized at CDC. All isolates were similar to human influenza A virus strains concurrently circulating in North America.

Other diagnoses included community-acquired pneumonia, bronchiolitis obliterans and organizing pneumonia, toxic shock syndrome, lymphoma, and rickettsial typhus ( Table 1 ). Among 28 patients without a diagnosis, 8 (29%) tested negative for influenza but had influenzalike illness and contact with an influenza A (H3)-positive person.

Among all reported patients, 52 (88%) had traveled to ≥1 of 11 countries in Asia with either confirmed human H5N1 cases or H5N1 in avian species before illness onset ( Table 1 ). Four (7%) patients with suspected H5N1 virus infection had not traveled outside the United States, but they had contact with recent travelers to Asia, and 1 had traveled to a country without confirmed H5N1 in poultry or wild birds. Although 14 (24%) reported having been within ≤1 m of any live poultry or domesticated birds in Asia, none reported touching live poultry, domesticated birds, or recently butchered poultry. No patients with suspected H5N1 virus infection had contact with any confirmed or suspected human H5N1 case-patients.


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