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From October 2005 through October 2006, 20 confirmed cases were reported from 12
provinces. Six cases were identified in 6 cities of 5 provinces; each city had an average
population of 8.3 million and was at least 112 km away from cities with another case (Figure 1).
More urban cases were reported in 2006 (5 [42%] of 12) than in 2005 (1 [13%] of 8), but this
difference was not statistically significant (p = 0.325) (Figure 2). Demographic and clinical
characteristics of the 6 urban patients with influenza (H5N1) cases are presented in Tables 1 and
2. All 6 urban patients were adults, median age 30 years (range 21 to 41); 5 died.
Five of the 6 urban case-patients had no direct contact with poultry. One patient prepared
freshly slaughtered chicken that she purchased for cooking at a live (wet) poultry market. No
patients kept poultry or other animals at home, and no poultry or poultry outbreaks were
identified in their neighborhoods. Five patients had visited wet poultry markets within a week of
illness onset, and all had visited a wet market during the 2 weeks before their illness. Three
patients visited wet markets at least once a day before illness onset. Only 1 patient (case-patient
5) had any travel history in the 2 weeks before illness onset. That patient had visited his parents?
home in a rural area, where healthy backyard poultry were kept outside the house, and he had
visited a wet market in the same area 2 weeks before illness onset (Table 2).
All 6 patients had no known contact with other confirmed influenza A (H5N1) patients or
with anyone with febrile respiratory symptoms. A total of 640 persons were followed up for
medical observation for 2 weeks, including 136 close contacts of the 6 patients, 389 healthcare
workers who provided care for them, and 115 persons who worked in the poultry markets visited
by the patients. Febrile respiratory illness developed in 5 contacts: case-patient 1?s mother, casepatient
3?s girlfriend, case-patient 6?s daughter, a nurse who cared for case-patient 6, and a
patient hospitalized on the same ward as case-patient 6. All 5 ill contacts recovered, and all
respiratory specimens collected from them tested negative for influenza A (H5N1) by reversetranscriptase?
PCR. Paired acute- and convalescent-phase serum samples collected from these 5
ill contacts tested negative for subtype (H5N1) neutralizing antibodies by microneutralization
assay.