Thursday, December 22, 2011

Iowa: No New trH3N2 Cases



H3N2 influenza virions –CDC PHIL


# 6028



Over the past few months we’ve been carefully watching the evolution and spread of a novel swine flu variant called trH3N2, that is a reassortment of the swine H3N2 virus that has acquired the Matrix (M) gene segment from the 2009 H1N1 virus.


So far, fewer than a dozen cases have been reported across 4 states - although the suspicion is that additional cases may have gone undetected.


While the majority of these cases reportedly had recent contact with swine, three recent cases out of Iowa were notable as they appear to be the result of Human-to-Human (H-2-H) transmission.


Nearly a month ago, the CDC released a special MMWR  dispatch that provided details on these three new cases, some background on earlier SOIV (swine origin influenza viruses) cases, and some analysis. 


A few excerpts follow (underscores & bolding mine), but follow the link to read the entire dispatch.


Limited Human-to-Human Transmission of Novel Influenza A (H3N2) Virus — Iowa, November 2011
November 23, 2011 / 60(Dispatch);1-3

On November 20, 2011, CDC confirmed three cases of swine-origin triple reassortant influenza A (H3N2) (S-OtrH3N2) virus infection in children in two counties in Iowa. None of the children were hospitalized, and each has recovered from a mild episode of febrile respiratory illness. All three were in contact with one another, and none had a known recent exposure to swine. No additional human infections with this virus have been detected in Iowa, and no evidence of sustained human-to-human transmission of this S-OtrH3N2 virus exists; surveillance is ongoing.

(Continue . . .)



Understandably, local health officials have been on increased alert, looking for more cases.  Overnight it’s been widely reported that, according to Iowa state health officials, no new cases  of this novel influenza virus have been seen since early November.


State Medical Director Dr. Patricia Quinlisk is quoted yesterday by The Des Moines Register (see New flu virus blips out of Iowa as quickly as it appeared) as saying the virus `apparently failed to continue spreading’.


Nonetheless, state health officials continue to be on watch for new cases


Surveillance isn’t perfect, of course, and relatively few people get tested when they get a flu-like illness. So it is possible (perhaps even likely) that there are some cases out there going undetected.


All of which makes it premature to sound the all-clear on this fledgling flu.


But this lack of new case detections in the face of enhanced surveillance would seem a pretty good indicator that this flu isn’t ready for prime time, and supports the CDC’s contention that there is no evidence of sustained human-to-human transmission of this S-OtrH3N2 virus.


As this trH3N2 virus has been detected in multiple swine herds, and in humans across four states, It would not be unreasonable to expect that we’ll see more cases of this novel flu crop up in the future.


The evolution of flu viruses is an ongoing process, and each new host infection presents the virus with another opportunity to evolve and change.


At some point, this virus may adapt well enough to human physiology to become a major player on the field of flu. Or it may simply fizzle out, and end up in evolution’s dustbin of failed mutations.


Influenza is notoriously unpredictable, and I certainly wouldn’t care to hazard a guess as to what happens next with this virus.

But for now, no flus is good news.

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