Occasional H7N9 case reports continue to filter in from Mainland China (Jiangxi Province reported a case on Saturday), but past 60 days has seen unexpectedly low numbers. Reporting from many provinces, however, has not as timely or a detailed as we’d like, leaving some doubt as to whether we are seeing the whole picture.
We may yet get another round of `bulk’ H7N9 announcements from the EOM epidemiological reports filed by the individual provinces near the middle of this month, but this year’s epidemic seems to be winding down.
That said, we’ve another H7N9 report - this time from Anhui Province – published by the Hong Kong Centre for Health Protection.
The Centre for Health Protection (CHP) of the Department of Health (DH) is today (May 6) closely monitoring an additional human case of avian influenza A(H7N9) in Anhui, and again urged the public to maintain strict personal, food and environmental hygiene both locally and during travel.
According to the Health and Family Planning Commission of Anhui Province, the male patient aged three in Huaibei had mild symptoms and was in stable condition. He had poultry exposure before onset.
From 2013 to date, 636 human cases of avian influenza A(H7N9) have been reported by the Mainland health authorities. Regarding the third wave in the Mainland since November 2014, a total of 196 cases have been reported, including 72 in Guangdong (see attachment for geographical distribution), 39 in Fujian, 38 in Zhejiang, 17 in Jiangsu, eight in Anhui, seven in Xinjiang, six in Shanghai, three in Jiangxi, two in Hunan, two in Shandong, one in Guizhou and one in Hubei.
The tally of 636 mainland cases provided by the CHP above represents only the `sickest of the sick’ – those ill enough to seek medical care and deemed ill enough to be tested for the virus.
Since H7N9 is capable of producing a broad range of symptoms in humans – ranging anywhere from asymptomatic or mild to severe pneumonia – the big unknown is how many cases go undetected in the community.
As with any disease, conventional surveillance and reporting can only reveal the tip of the pyramid.
Despite their obvious limitations, passive surveillance systems can often tell us if an outbreak is trending up or down - or spreading to new geographic areas - and it affords an opportunity for epidemiologists to test contacts of known cases to look for signs of human-to-human transmission.