Credit CDC
# 8153
Foshan City, located about 85 miles from Hong Kong and nestled on the outskirts of the sprawling provincial capital of Gaungzhou, has already reported two H7N9 cases since the New Year (see WHO Update On 7 Recent H7N9 Human Cases In China). Those first two cases were listed on Thursday by the WHO as being in critical condition.
Today, the Guangdong Province Ministry of Health reports two additional cases in Foshan City, but unlike the first two cases, these patients are being described as suffering only `mild’ illness.
First, the announcement, after which I’ll return with more on the issue of `mild’ or asymptomatic H7N9 infection.
Foshan report two cases of human infection with the H7N9 avian influenza mild cases
2014-01-10 16:00:59 Ministry of Health and Family Planning Commission
January 10 afternoon, the Provincial Health and Family Planning Commission informed Foshan confirmed two cases of human infection with the H7N9 avian influenza. Two cases are mild, sporadic cases, no epidemiological link.
Case 1 Liu, female, 42 years old, lives in the town of Yanbu, Nanhai District, Foshan City. Engage in wholesale sales of live poultry. January 5, 2014 the disease, January 8 to local hospitals infected with H7N9 fever clinic, give "Tamiflu" treatment, January 9 admitted to the hospital. Currently the patient has fever, mild symptoms. Local health departments for 20 close contacts under medical observation and found no abnormalities.Case 2 Liu, female, 59 years old, currently residing in Nanhai District of Foshan street, no live poultry exposure history. December 29, 2013 the disease, avian influenza H7N9 infection in sentinel local hospital Jan. 2, 2014, to "Tamiflu" treatment. Currently, patients with mild symptoms. Local health department for five close contacts under medical observation and found no abnormalities.
Since August 2013 the first reported case in Huizhou since, as of January 10, 2014, the province reported a total of 12 cases of patients were cured in 2 cases, 1 death (residence Dongguan). By patient place of residence, Shenzhen two cases, four cases in Foshan, Huizhou one case, two cases in Dongguan, Yangjiang 3 cases.
The oft seen graphic at the top of this post illustrates that official numbers of nearly any disease you care to mention only represent the `tip of the pyramid’, since (depending upon the illness’s severity, the accuracy of testing, and the population’s access to those tests) only a portion of those afflicted will be tested and counted.
It is also axiomatic that we are more likely to test those experiencing serious illness, as they tend to go to hospitals more frequently. This can often skew our perception of the severity of an emerging virus, particularly in the beginning.
Most viral illnesses can produce a wide spectrum of symptoms, ranging from mild or even asymptomatic presentation, to severe and/or life threatening. So the great unknown with H7N9 (and with just about any other emerging infectious disease) is how many mild, or asymptomatic cases go uncounted?
Last year we saw several attempts to estimate the likely number of H7N9 cases in China.
Last April, in H7N9: Trying To Define The Size Of The Iceberg, University of Hong Kong researchers announced that they believed the actual number of cases was at least twice the number being reported.
A few weeks later, the Eurosurveillance Journal carried a rapid communications from researchers at the University of Hong Kong, where they announced the likely number of cases to be several times higher than reported.
8, Issue 19, 09 May 2013
B J Cowling , G Freeman, J Y Wong, P Wu, Q Liao, E H Lau, J T Wu, R Fielding, G M Leung
Between 31 March and 21 April 2013, 102 laboratory-confirmed influenza A(H7N9) infections have been reported in six provinces of China. Using survey data on age-specific rates of exposure to live poultry in China, we estimated that risk of serious illness after infection is 5.1 times higher in persons 65 years and older versus younger ages.
Our results suggest that many unidentified mild influenza A(H7N9) infections may have occurred, with a lower bound of 210–550 infections to date.
By mid-summer, another analysis (by the same researchers) appeared in The Lancet (see Lancet: Clinical Severity Of Human H7N9 Infection) that substantially raised their estimate of the total number of H7N9 cases in China. In this new study (after citing many limitations to the data) they write:
Our estimate that between 1500 and 27 000 symptomatic infections with avian influenza A H7N9 virus might have occurred as of May 28, 2013, is much larger than the number of laboratory-confirmed cases.
The accuracy of these estimates is unknown, but it is very likely that the official case counts under-represent the real burden of H7N9, perhaps by a sizable margin.
Estimates aside, the fact that only a few small family clusters have been documented and we haven’t seen evidence of ongoing transmission among the close contacts of the cases we know about, makes a pretty good prima facie case that the virus does not yet possess the ability to transmit efficiently between humans.
That could change, of course.
Which is why we watch these outbreaks in China carefully, looking for any signs that the behavior of this virus is changing.
