Understanding 'Bird Flu' Patients

H7N9 bird flu cases and possible source investigated in China

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) News has been developing fast from the H7N9 bird flu outbreak in China. But what do we know about the patients who have been infected with the disease? Are there common threads in these cases?

A team of Chinese researchers took an in-depth look at the 82 cases identified between March 25 and April 17, 2013.

The results showed that most patients had recently been exposed to animals, which led the researchers to suspect infected poultry as the source of the virus.

"Avoid touching your face to slow the spread of germs."

The study was led by Qun Li, MD, from the Public Health Emergency Center at the Chinese Center for Disease Control and Prevention (CCDC) in Beijing.

Dr. Li and team looked at data from field investigations of the flu that were reported to the CCDC before April 17. Medical records were also reviewed and interviews were conducted. Interviewees included people in close contact with the patients, including relatives and healthcare workers who treated patients.

After analyzing the data, the researchers found that the average age of H7N9 patients was 63 years old, and that 46 percent of patients were 65 or older. By contrast, only two patients (2 percent) were younger than 5 years old, and both of those cases were deemed “mild.”

Most of the patients were male (73 percent) and living in urban areas (84 percent). Of the 71 patients with available data, 54 (76 percent) had underlying medical conditions.

“Most of the patients with confirmed H7N9 virus infection were considered to be at increased risk for complications from influenza owing to age or the prevalence of certain underlying medical conditions,” the authors wrote.

Information about the patients’ contact with animals was known for 77 of the 82 patients, and 59 (77 percent) of these patients reported recent exposure to animals when visiting or working at a live animal market. Forty-five patients had recently been exposed to chickens, 12 to ducks and four to swine.

“Four of the patients with confirmed cases (5 percent) worked as poultry workers: 3 slaughtered poultry at a live poultry market, and 1 transported live poultry,” the authors reported.

Although more research is needed, the authors suspect that infected poultry is the source of the disease. While large numbers of confirmed patients reported recent exposure to animals, monitoring of close human contacts did not prove to uncover further cases.

The researchers identified close contacts of the victims and monitored them for seven days. The contacts were watched for symptoms. If symptoms were present, throat swabs were taken to test for H7N9.

“Close contacts were defined as individuals known to have been within 1 m, or had direct contact with respiratory secretions or faecal material, of a patient with confirmed H7N9 virus infection any time from the day before the onset of illness to when the case was isolated in the hospital,” the authors wrote.

As of April 17, 1,251 contacts had been monitored for seven days. Symptoms developed in 19 people (1.5 percent), and throat swabs were collected. All of the throat swabs tested negative for H7N9.

There had been three “family clusters” of the disease identified by April 17. Researchers are still trying to understand these groups.

The authors reported that in two of the clusters, “limited human-to-human transmission of H7N9 virus after close, prolonged, unprotected contact with a symptomatic patient with suspected H7N9 virus infection remains a possibility.”

However, one patient with a suspected case died before testing could be confirmed and the other case is still being investigated, so the matter has yet to be confirmed.

According to the researchers, “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.”

Dr. Li and team reported that the mortality rate as of April 17 was 21 percent, “but since many of patients with confirmed H7N9 virus infection remain critically ill, we suspect that the mortality may increase.”

The researchers found that the average time between onset of symptoms and hospitalization of patients was 4.5 days (this data was available for 81 of the 82 patients). Of the 17 patients who died, the average time between onset of illness and death was 11 days.

According to the authors, the information seen so far suggests that H7N9 “is more virulent in humans than are other H7 viruses.”

There is still much to be understood about this strain of avian influenza and the authors stressed, “This is an ongoing investigation.”

The report was published online on April 24 by The New England Journal of Medicine. The latest information available from the World Health Organization (WHO) on April 25 reported a total of 109 infections and 22 deaths from the virus.

Reviewed by: 
Review Date: 
April 26, 2013
Last Updated:
November 14, 2013