H7N9 cases show no epidemiologic link
Researchers with the Chinese CDC reported that most people with influenza A(H7N9) infection had severe lower respiratory tract illness and a history of recent exposure to poultry, but they were otherwise epidemiologically unrelated.
The risk for human-to-human transmission of the virus is still low, but researchers could not rule out limited human-to-human transmission in four family clusters, according to the report in The New England Journal of Medicine.
As of Feb. 11, there have been 330 cases of H7N9 throughout China, and 65 deaths since the first human infection was identified in February 2013.
The investigators conducted field investigations for confirmed cases of H7N9 infection to obtain data on demographics, exposure history and illness timeliness. They also monitored close contacts of the cases and obtained throat swabs from those who developed symptoms to test for H7N9.
The analysis includes the 139 confirmed cases as of Dec. 1. The median age was 61 years, 73% of the cases were men and 73% were urban residents. Twelve areas, including 10 provinces and two municipalities, had confirmed cases. Nine of the confirmed cases were poultry workers and 82% of the 131 people with data had a history of exposure to live animals. Among those, 82% were exposed to chickens.
One hundred thirty-seven patients (99%) were hospitalized. Of the 103 with available data, 65 were admitted to an ICU. Pneumonia or respiratory failure developed in 125 patients. Forty-seven hospitalized patients died after a median illness duration of 21 days; 88 were discharged and two remain hospitalized.
To track secondary cases, 2,675 close contacts of the cases were monitored. Twenty-eight developed respiratory symptoms, but all tested negative for H7N9.
“The spread of H7N9 virus among poultry is likely to increase during the winter and spring months, with the potential for increased transmission to exposed persons,” the researchers wrote. “Therefore, enhanced surveillance for H7N9 virus among poultry and people, investigations of close contacts of confirmed cases, and virologic analyses to assess genetic changes that might suggest increased transmissibility among humans are all critical to informing prevention and control efforts and assessing the pandemic potential of this H7N9 virus.”
Disclosure: The researchers report no relevant financial disclosures.