H7N9 Mortality

A week ago, in response to some scary reports, I tweeted this:

I wanted to see how my public prediction held up in the H7N9 outbreak after an admittedly short 7 days and approximately 2 weeks after the outbreak gained widespread attention. To do this, I simply plotted the reported mortality rate using the daily case and mortality counts available through the @WHO twitter feed between April 1st and April 16th.

While the case counts have gone from 3 to 63 over this period, reported deaths have risen more slowly from 2 to 14 and the mortality rate has fallen from 67% to 22%. When I made the prediction it was 30%. If I had included data from April 17th, the mortality rate would have fallen further to 20.7%, 17 deaths and 82 cases. I've plotted the daily mortality rate below. Good news, but still a ridiculously virulent virus. Hopefully, as more surveillance specimens return, the mortality rate will continue to fall. Hopefully.

Addendum: Immediately after posting this, several twitter discussions began. To clarify, I know many of the sick patients are still hospitalized in the ICU. Even cases that appear to initially recover could succumb to secondary bacterial infections. Helen Branswell made the important observation that two of the three cases in the recent NEJM report were infected with Carbapenem-resistant Acinetobacter baumannii and at least one of them didn't appear to receive appropriate antibiotic therapy. Hopefully, as recognition increases, so will early diagnosis and early antiviral therapy along with effective antibiotic therapy (if available).

Influenza at the “human-animal interface”

The first three novel avian influenza A (H7N9) viruses have been sequenced, and the sequences uploaded to the Global Initiative on Sharing All Influenza Data (GISAID). Not surprisingly, there were genetic changes found that have been associated with increased transmissibility of other avian flu strains to mammals.

I have no deep thoughts on this--it is what influenza does, after all, with avian and other non-human strains occasionally making the leap to humans. The few things we know about this particular strain, as of late yesterday, can be found at the CDC and WHO websites, and include the following:

• a total of 21 cases have been laboratory confirmed in China, including six deaths, 12 severe cases and three mild cases
• more than 530 close contacts of the confirmed cases are being closely monitored
• the viruses isolated to this point appear to be susceptible to neuraminidase inhibitors (e.g. oseltamivir) but resistant to adamantanes (e.g. amantidine, rimantadine)
• there is no current evidence of “ongoing human-to-human transmission"
• the virus should be detectable with existing PCR methods as an “unsubtypeable” influenza A virus (the CDC is working on adding this strain to their testing approach so that it can be more quickly subtyped if it spreads outside of China)

The most recent interim guidance for case investigation, testing, infection control and treatment are here.

Finally, for those interested in a regular update on the threat of non-human flu strains, the WHO publishes monthly updates on “influenza at the human-animal interface” (wait, aren’t Homo sapiens also animals? Maybe it should be, “influenza at the human-nonhuman interface”…).

Animals

Those of you who follow our Facebook page have noted several recent stories on the zoonotic disease front. New human cases were reported of the influenza A (H3N2) variant, a swine virus that thus far appears to cause mild disease and has limited-to-no transmissibility from human-to-human (virtually all cases have been among those with direct pig contact, often at summer fairs). Meanwhile, an avian H3N8 strain was reported to be the cause of a recent fatal outbreak of pneumonia among New England harbor seals—whenever an avian strain demonstrates adaptation to a mammalian host, it is cause for concern. This development further stresses the importance of open and transparent work to understand the key features of virulent influenza strains that predict human infection and transmission (in other words, lift the “voluntary moratorium”). Finally, we have a very provocative report suggesting that rabies virus exposure, at least in remote communities in the Peruvian Amazon, may not always result in infection and death. Rabies is notorious for having a human fatality rate approaching 100%, with very few reports of survival after clinical infection. It is surprising, then, to find evidence for nonlethal rabies virus infection among those with bat exposure and no history of vaccination. Too soon, really, to determine if this finding is explained by unique genetic-immunologic characteristics of this remote population, or if there are other mechanisms of nonlethal exposure that have not yet been identified.

While we are on the topic, I’d like to plug my favorite blog about infections in animals, Worms and Germs, by Drs. Scott Weese and Maureen Anderson of the Ontario Veterinary College's Centre for Public Health and Zoonoses.