|Credit HK CHP|
The wide spectrum of illness caused by avian H7N9 in humans is clearly illustrated by the two very different outcomes from last week's cases in Hong Kong and Macao.
The 58 y.o. poultry trader in Macao never showed symptoms, and was proclaimed free of the virus on Saturday, whereas the 75 y.o. man in Hong Kong was listed in critical condition when we learned of his infection.
Today, the HK CHP has released the following short statement:
In response to media enquiries, the Centre for Health Protection (CHP) of the Department of Health today (December 27) reported an update on the first imported human case of avian influenza A(H7N9) in Hong Kong this winter.
The CHP noted that the 75-year-old man, confirmed human case of avian influenza A(H7N9), who was admitted to North District Hospital on December 9 for management passed away on December 25.Ends/Tuesday, December 27, 2016Issued at HKT 14:25
While age differences, medical histories and comorbidities, and even the type and extent of exposure may account for these two very different outcomes, exactly why some people can fight off this infection without apparent illness and others struggle to survive is unknown.
Mild or asymptomatic infections such as we saw in Macao remind us that the `official' number of H7N9 infections in China is likely a serious undercount.
Most people with mild to moderate influenza never seek medical care (where they are likely to be tested), and some serious or fatal cases are likely missed by surveillance as well.
Early estimates of the incidence of H7N9 in China (see Lancet: Clinical Severity Of Human H7N9 Infection) suggested the real number might be 10 to 100 times greater than reported.
This becomes all the more important during the winter seasonal flu epidemic, when other - already human adapted - influenza A viruses (H3N2 & H1N1) co-circulate with these avian viruses.
While it doesn't happen often, we know that humans can be infected by two influenza A viruses at the same time, and very rarely, that can lead to the generation of a `reassorted' virus - one that contains genetic material from both viruses.
With both H5N6 and H7N9 circulating in China, H5N6 now in Japan and Korea, and both H5N8 and H5N1 making serious inroads in Europe, the Middle East, and Africa - plus a plethora of swine variant viruses - the odds of a chance hook up between a novel and seasonal flu virus is going up.
Granted, most reassortant viruses are evolutionary failures, unable to compete with existing `wild' viruses. But every once in a great while a new hybrid will emerge with genuine pandemic potential, and so the risks cannot be discounted.
For more on co-infection in humans and reassortment, you may wish to revisit: