While this winter’s reporting of H7N9 cases out of many of China’s provinces seems suspiciously slow (see Jiangsu Province’s Uncertain H7N9 Count), Guangdong Province has provided almost daily reports of new cases over the past week.
Today Hong Kong’s CHP has been notified of 2 more confirmed infections, making 9 (actually 10, if you count HK’s imported case) from Guangdong Province over the past 7 days.
First today’s update from Hong Kong’s Centre For Health Protection, then I’ll be back with a little more.
The Centre for Health Protection (CHP) of the Department of Health (DH) is today (January 25) closely monitoring two additional human cases of avian influenza A(H7N9) notified by the Health and Family Planning Commission of Guangdong Province (GDHFPC), and again urged the public to maintain strict personal, food and environmental hygiene both locally and during travel.
According to the GDHFPC, the male patient aged 62 in Dongguan and the female patient aged 78 in Shanwei were hospitalised for management. The male patient is in critical condition while the female patient in serious condition.
To date, 493 human cases of avian influenza A(H7N9) have been reported by the Mainland health authorities, respectively in Zhejiang (146 cases), Guangdong (131 cases), Jiangsu (63 cases), Shanghai (44 cases), Fujian (28 cases), Hunan (24 cases), Anhui (17 cases), Jiangxi (nine cases), Xinjiang (nine cases), Shandong (six cases), Beijing (five cases), Henan (four cases), Guangxi (three cases), Jilin (two cases), Guizhou (one case) and Hebei (one case).
Since H7N9 is capable of producing a broad range of symptoms in humans – ranging anywhere from asymptomatic or mild (see Concerns Over Asymptomatic H7N9 Case In Beijing) 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.
Simply put, those who are the most severely affected are the ones most likely to seek medical care, and are therefore more likely (but not guaranteed) to be tested for H7N9. Being sicker, they are also more likely to succumb to the disease.
Inevitably, passive surveillance systems pick up `the sickest of the sick’, while mild or moderate infections in the community go untallied, skewing our perception of the mortality rate of the virus.
Attempts have been made to estimate the total size of the H7N9 pyramid (see Lancet: Clinical Severity Of Human H7N9 Infection), but the accuracy of these estimates is unknown.
Despite their obvious limitations, the passive surveillance systems being used can often tell us if the 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.
Useful information, as long as you take it with a large grain of salt.