H7N9 Influenza: Most Patients Critically Ill

Troy Brown

April 25, 2013

Most of the 82 patients studied who developed H7N9 became critically ill and were epidemiologically unrelated, according to an analysis of data obtained from field investigations of cases that occurred in China before April 17, 2013. Human-to-human transmission between close contacts has not been confirmed but could not be ruled out in 2 families in an analysis by a group of researchers from China and the Centers for Disease Control and Prevention.

Qun Li, MD, from the Public Health Emergency Center in China, and colleagues present their findings in an article published online April 24 in the New England Journal of Medicine.

The researchers defined a confirmed case as one verified by H7N9 virus presence by positive real-time reverse-transcriptase-polymerase-chain-reaction (RT-PCR), viral isolation, or serologic testing. Close contacts were observed for 7 days. The investigators obtained throat swabs from symptomatic contacts and tested for the H7N9 virus by real-time RT-PCR.

Among the 82 confirmed cases, the median age was 63 years (range, 2 - 89 years): 38 cases (46%) occurred in patients aged 65 years or older and 2 (2%) in children younger than 5 years. Both children had clinically mild upper respiratory illness. Two suspected cases were also found.

Of the confirmed cases, 73% were male, and 84% were urban residents. Of the 71 patients with available data, 54 (76%) had underlying medical conditions. Cases were reported in 6 areas of China.

Eighty-one patients with confirmed disease (99%) were hospitalized and 17 (21%) confirmed cases, and a single suspected case died of acute respiratory distress syndrome or multiorgan failure. A total of 60 confirmed cases and 1 suspected case remained critically ill as of April 17; 4 patients were discharged from the hospital, and 1 child was never hospitalized.

Animal Exposure

Animal exposure data were available for 77 of the confirmed cases. Of these patients, 59 (77%) had recent animal exposure: 45 (76%) to chickens, 12 (20%) to ducks, and 4 (7%) to swine. The individuals had either worked at or visited a live animal market. These patients also reported exposure to pigeons, geese, quail, wild birds, pet birds, cats, and dogs. History of animal exposure was unclear for the remaining 5 patients, in whom investigations were still ongoing.

The researchers estimated the median incubation period was 6 days in 23 patients for whom detailed data were available.

Of the 1689 close contacts, 1251 completed the 7-day monitoring period. A few (19; 1.5%) developed respiratory symptoms, but they all tested negative for the H7N9 virus.

There were 2 family clusters in which human-to-human transmission could not be ruled out. In one, a brother and his father were in prolonged, close contact with the index case. The father and brother cared for the index case and ate meals together. The index case had contact with live poultry, but the father and brother did not.

In the other family, a father had suspected illness and his daughter had prolonged, close, unprotected contact with him. She was later confirmed to have H7N9 illness. The father had contact with live poultry, but the daughter had no contact with poultry or pigs.

The investigators had data regarding oseltamivir administration for 64 patients, of whom 41 (64%) received oseltamivir starting a median of 6 days after illness onset.

"Although the risk of human-to-human transmission of H7N9 virus appears to be low, the actual risk is currently unknown, and the Chinese national guidelines recommend implementing control measures, such as prompt isolation of the patient, active monitoring of close contacts, and implementation of standard, contact, and droplet precautions by health care personnel in hospitals," the authors write.

"In addition, national guidelines recommend that antiviral treatment with oseltamivir should be administered as soon as possible in patients with suspected or confirmed cases of H7N9 virus infection," they conclude.

The China–US Collaborative Program on Emerging and Re-emerging Infectious Diseases provided financial support to a number of individuals and institutions for travel and accommodation fees for fieldwork, attendance at an investigator meeting, equipment, and fees for manuscript preparation. Two researchers reported employment at Jiangsu Provincial Center for Disease Control and Prevention. Two researchers received consulting fees from and 2 researchers reported employment by the China–US Collaborative Program on Emerging and Re-emerging Infectious Diseases. Two researchers reported receiving fees for travel to major meetings for the past 3 years.

N Engl J Med. Published online April 24, 2013. Full text