Two detailed reports on H7N9 avian flu transmission among family members, including an event that occurred during the second wave of infections, provides reassuring signals that the virus doesn't often spread among humans, Chinese researchers noted yesterday.
Reports of family clusters since H7N9 emerged last spring have been rare, and global health groups have said the main source of infection appears to be from poultry and their environments, though some human-to-human transmission is likely when people have extended, unprotected contact with sick patients.
The investigations center on a wife and husband from Shanghai who both died from their H7N9 infections during the outbreak's first wave and a man in his late 20s and his young son from Guangdong province who got sick during the second wave.
Both investigations included contact tracing, poultry and environmental sampling at nearby markets, and genetic analyses of H7N9 viruses that were isolated. Both reports appeared yesterday in the latest issue of Eurosurveillance.
Infections in wife, husband
The first report describes an H7N9 infection in a Shanghai woman in her early 50s who got sick in late March of 2013 when the first cases were being detected. She was previously healthy and had often bought pork and vegetables at a nearby market that also sold live poultry.
The woman's husband, in his middle 50s, started having symptoms on Apr 2 after taking care of his wife at home and participating in her care while she was hospitalized. He had not eaten or bought live poultry in the 2 weeks before he got sick.
Both patients were hospitalized with severe pneumonia. The woman died on Apr 2, and her husband died on Jun 26.
Tracing of 27 close contacts, which included 22 health workers, found only one who had flulike symptoms. The contact was the woman's sister, who had helped care for her and cleaned her corpse without wearing personal protection. However, tests for H7N9 were negative.
Sampling at the market the woman shopped at, and another that got its chickens from the same wholesaler, yielded five positive test results for H7N9, including four from a chopping board and one from chicken feces. No birds were at the markets, because Shanghai officials had just ordered temporary closures to curb the spread of the new virus.
Samples from homing pigeons raised near the couple's home were negative for the virus.
The research team said several findings are consistent with a family cluster of avian influenza. Her husband got sick 6 days after his wife did, and he had close contact with her during each of those days. The man hadn't gone to a market or eaten poultry 2 weeks before he got sick, and pigeons near the couple's community tested negative for H7N9. Also, genetic analysis of samples from the wife and her husband were highly similar.
Unlike other family avian flu clusters, the woman and her husband weren't genetically related to each other, which they said may shed light on the risk of prolonged close contact in H7N9 infections and shows that more research is needed to better understand genetic susceptibility to influenza infection.
The index patient in the second report is a man in his late 20s from Guangzhou, the capital of Guangdong province. The man got sick in early January 2014 and was reported as the province's first H7N9 case-patient. His 5-year-old son got sick 10 days after his father started having symptoms.
The man was hospitalized for a severe H7N9 infection and eventually recovered. His son had a mild version of the illness in the wake of having had prolonged unprotected contact with his father while he was sick.
Investigators found that the man had worked long hours in a market at a tofu stall that was adjacent to an area where poultry were unloaded every morning. He had not bought or cooked poultry in the 12 days before he became ill and he had not been around any sick people. The boy's grandparents said he had not been to any markets or had any contact with poultry in the 12 days before he got sick.
Health officials identified 40 close contacts for medical monitoring. No other H7N9 infections were found, even in the man's wife, who had provided unprotected care at home and at his hospital bedside. Serologic sampling of 15 poultry workers at the market showed no signs of previous infection.
Of 26 environmental samples taken from four live-poultry stalls at the market, one from a chopping block and one from bloody sewage tested positive for H7N9.
Genetic analysis of H7N9 viruses from the man, his son, and the environment found identical sequences, with several features the same as H7N9 viruses isolated during the first wave, including positions on the cleavage site, receptor binding sites, and glycosylation motifs.
Researchers found that the hemagglutinin gene was more than 99% similar to a strain isolated early from chickens in the same city, which they said strongly points to the contaminated live-bird market as the source of the man's infection.
They said several factors point to the father being the source of the boy's infection, including reports that the boy had not been to markets or had contact with poultry and had intensive contact with his dad while his dad was ill, as well genetic similarity of the H7N9 viruses.
The team concluded that the findings support the notion that person-to-person H7N9 infections can occur, especially in closely related people. However, they noted that some of the other family members who were closely related did not get sick, despite similar close contact.
Though the H7N9 virus seems to have limited capacity for human-to-human spread, ongoing reassortment requires close surveillance for any changes, the authors wrote.
Experts weigh implications
In an editorial that accompanies the two reports and other avian influenza studies published in the same issue of Eurosurveillance, two researchers from Erasmus Medical Center in the Netherlands wrote that all the reports highlight the importance of zoonotic viruses on global health.
The experts are Sander Herfst, PhD, and Ron Fouchier, PhD, with the center's virology department.
They wrote that little is known about how viruses transmit, and the knowledge gaps raise big questions for public health, such as the potential for a newly emerging virus to trigger a pandemic.
"Currently, we appear to rely on humans as sentinels for virus outbreaks in animals and often apply a reactive rather than pro-active approach to limit the impact of emerging virus infections," Herfst and Fouchier wrote.
They added that implementing a "One Health" approach could help improve detection and surveillance in both animals and people and might limit the impact of future pandemic threats.
Hu J, Zhu Y, Zhao B, et al. Limited human-to-human transmission of avian influenza (H7N9) viruses, Shanghai, China, March to April 2013. Eurosurveill 2014 Jun 26;19(25):pii=20838 [Full text]
Xiao XC, Li KB, Chen ZQ, et al. Transmission of avian influenza A (H7N9) virus from father to child: a report of limited person-to-person transmission, Guangzhou, China, January 2014. Eurosurveill 2014 Jun 26;19(25):pii=20837 [Full text]
Herfst S, Fouchier R. Epidemiological and genetic investigations of human-to-human transmission of zoonotic influenza viruses. (Editorial) Eurosurveill 2014 Jun 26;19(25):pii=20840 [Full text]