The World Health Organization has posted a new update on H7N9 cases from China, covering the period from May 7th-May 22nd.
While this year's H7N9 winter-spring outbreak has chalked up fewer overall cases than the past couple of seasons, we have seen some subtle signs of change in the virus's behavior.
Enough so that the WHO changed their long standing Risk Assessment in March of this year from:
If the pattern of human cases follows the trends seen in previous years, the number of human cases may rise over the coming months. Further sporadic cases of human infection with avian influenza A(H7N9) virus are expected in affected and possibly in the neighboring areas. Should human cases from affected areas travel internationally, their infection may be detected in another country during travels or after arrival. If this were to occur, community level spread is considered unlikely as the virus has not demonstrated the ability to transmit easily among humans.
To the slightly more cautious risk assessment you'll find below. First today's update, after which I'll have a bit more on some of these changes.
Human infection with avian influenza A(H7N9) virus – China
Disease outbreak news
1 July 2016
On 15 June 2016, the National Health and Family Planning Commission (NHFPC) of China notified WHO of 5 additional laboratory-confirmed cases of human infection with avian influenza A(H7N9) virus, including 1 death.
Onset dates range from 7 May to 22 May. The cases range in age from 45 to 63 years, with a median age of 53 years. Of these 5 cases, 4 (80%) are male. The majority (4 cases, 80%) reported exposure to live poultry, slaughtered poultry or live poultry markets. No human to human transmission was reported.
Cases were reported from 4 provinces: Jiangsu (2), Beijing (1), Hebei (1) and Jiangxi (1).
Public health response
The Chinese Government has taken the following surveillance and control measures:
- strengthening outbreak surveillance and situation analysis;
- reinforcing all efforts on medical treatment; and
- conducting risk communication with the public and dissemination of information.
WHO risk assessment
Most human cases are exposed to the A(H7N9) virus through contact with infected poultry or contaminated environments, including live poultry markets. Since the virus continues to be detected in animals and environments, further human cases can be expected.
Although small clusters of human cases with influenza A(H7N9) viruses have been reported previously including those involving healthcare workers, current epidemiological and virological evidence suggests that this virus has not acquired the ability of sustained transmission among humans. Therefore, community level spread of this virus is considered unlikely for the time being.
Human infections with the A(H7N9) virus are unusual and need to be monitored closely in order to identify changes in the virus and/or its transmission behaviour to humans as it may have a serious public health impact.
The H7N9 virus is constantly changing, and as of more than a year ago had evolved into at least 48 genotypes in China (see Nature: Dissemination, Divergence & Establishment of H7N9 In China).
Over the four winter epidemics, we've seen small signs that the virus's behavior may be changing as well. In 2015's EID Journal: The Transmission Potential Of A(H7N9) In China, the authors found that while no evidence of sustained transmission was detected, they noted:
- `evidence of a small but significant amount of transmission between humans in the first and second waves’
- `evidence of increased transmission potential in the second wave
While this past May, in EID Journal: Human Infection With H7N9 During 3 Epidemic Waves - China, researchers found patients hospitalized in the 2nd and 3rd wave with severe H7N9 tended to be younger, and from more rural areas, than those from the 1st wave.
They also found that the risk of death among hospitalized patients was greater in the second and third waves, although that varied between provinces.
Last weekend, in Differences In Poultry Exposure Between Human H7N9 and H5N1 Infection, we saw an analysis that suggested that poultry contact may play less of a role in human infection than previously thought.
And perhaps most importantly, we've seen an increase in the number of small clusters - including hospital transmission - over the past couple of years. A sampling of related blogs include:
EID Journal: Nosocomial Co-Transmission Of H7N9 & H1N1pdm09
NEJM: Probable Hospital Cluster of H7N9 - China, 2015
And last march, in WHO H7N9 Update Details 3 Clusters In China, we saw - out of 29 cases reported during February - 3 family clusters involving a total of 6 people.
None of which means that H7N9 is ready for prime time, but it does remind us that with influenza, the only constant is change.