Last November’s outbreak of drug-resistant H1N1 among four patients at Duke University Medical Center likely occurred through patient-to-patient transmission, according to a report released Saturday.

Five Duke physicians joined the Centers for Disease Control and Prevention and the North Carolina Division of Public Health to examine the nature of the outbreak, which CDC confirmed Nov. 23, 2009. The report was presented Saturday at the Fifth Decennial International Conference on Healthcare-Associated Infections in Atlanta.

“We found that the oseltamivir-resistant H1N1 influenza was isolated to the four patients,” Dr. Luke Chen, DUMC infectious diseases specialist, told WRAL. “There was no evidence of spread to additional patients or caregivers on the affected ward.”

According to the report, four patients were admitted to the hematology-oncology ward late last September for reasons unrelated to influenza infection. After one patient experienced fever, however, the remaining three patients became infected one, three and five days after the first onset of influenza-related illness.

The study also reported that all four patients were ambulatory and capable of interacting outside their rooms before they were infected. Three patients were located in adjacent rooms.

Chen told WRAL that influenza can often be hidden under other conditions, and influenza diagnoses are difficult because many patients have other medical problems that may produce fever or respiratory symptoms.

“One key thing we can learn from this outbreak is that all clinicians and health care workers should suspect the diagnosis of influenza even among very ill patients who have multiple medical problems,” Chen said.

The report concluded that increased vigilance and aggressive isolation are necessary to limit potential transmission of H1N1.

Medical administrators at Duke could not be reached for comment Sunday.