# 8262
The World Health Organization published updated case count maps and epi curve charts on the H7N9 virus over the weekend that are current as of 1/30/2014, that give us an opportunity to compare last spring’s first wave with the current (and ongoing) wave of cases in China.
The first chart, the epi curve, shows that as of the cutoff date, both outbreaks were roughly the same size although the second outbreak shows no signs of ending anytime soon.
A side-by-side look at the case count maps shows a distinct shifting of cases towards the southern provinces in this second wave, bringing the virus to Hong Kong’s doorstep, and closer to the (often porous) border with Vietnam.
Other trends we are seeing in this second wave are a slightly younger demographic and slightly more female cases than last spring, although cases are still skewed heavily towards older males males.
Credit ECDC H7N9 Rapid Risk Assessment Feb 2014
This epidemiological analysis from last week’s WHO H7N9 Background & Summary Report.
Epidemiology
The laboratory-confirmed cases have been reported from 13 provinces/municipalities in eastern mainland China, Hong Kong, Special Administrative Region, China, and the Taipei Centers for Disease Control (Taipei CDC). Most cases are presumed to have contracted the infection directly from infected animals or their environment, particularly as a result of visiting live animal markets. Only a few small clusters with possible human-to-human transmission have occurred among family members, but there has been no evidence of sustained human-to-human transmission to date.
As of 28 January 2014, the case fatality rate of all confirmed cases is 22%, but many cases are still hospitalized. Of all cases, 67% were male. The median age of reported cases is 58 years and that of fatal cases is 66 years.
Cases occurred in a first wave (n=133) from February through May 2013. Reports of human infection decreased during the summer, with only two cases reported; they have increased since October, demonstrating a second wave, likely in conjunction with cooler temperatures.
Unknown in all of this is how many mild, or asymptomatic cases have gone undetected.
The assumption is – based on practically every other viral disease we’ve seen – that the cases being reported are a subset of the total; the so called `tip of the pyramid’.
Credit CDC
While attempts have been made to estimate the total size of the pyramid (see Lancet: Clinical Severity Of Human H7N9 Infection), the accuracy of these estimates is unknown, and we probably won’t get a good handle on that until extensive seroprevalence studies can be conducted across Eastern China.
The good news in all of this is that after the first wave, we saw an impressive avalanche of research papers come out of China on this emerging virus last summer, and I fully expect we’ll see a repeat again this summer. Meaning that we should know a lot more about this virus six or eight months from now than we do today.
