Wednesday, September 14, 2011

CDC Update On Recent Novel Swine Flu Cases



Reassortant H3N2 virus detected in Pennsylvania & Indiana – Source CDC

# 5840


Off and on for several years, and most recently over the past couple of weeks, we’ve seen sporadic reports of novel swine flu infections in humans around the United States (separate and apart from the 2009 H1N1 virus).   


The number detected since 2005 is very small; only 25.


But in recent weeks 4 cases resulting from a reassorted H3N2 swine virus (with a gene borrowed from the 2009 H1N1) have shown up in Indiana (1) and Pennsylvania (3) prompting an epidemiological investigation.


Earlier blogs on these developments include:


Pennsylvania DOH: Updated FAQ On The Novel Swine Flu Cluster
Pennsylvania Reports 2 More Novel Flu Cases
MMWR: Swine-Origin Influenza A (H3N2) Virus Infection in Two Children



As I wrote yesterday in What Lies Beneath, it likely that very limited human-to-human transmission of this virus may have occurred, but the virus does not appear capable of sustained and efficient transmission among humans at this time.


The concern, of course, is that could change over time.


Below you’ll find the the CDC’s updated SOIV (Swine Origin Influenza Virus) page that reflects this ongoing investigation (reformatted for readability)



Reported Human Infections with Swine-Origin Influenza Viruses (SOIV) in the United States since 2005

As of September 9, 2011, 25 cases of human infection with swine origin influenza viruses have been reported in the United States. These are viruses that normally infect pigs. Like human influenza viruses, there are different subtypes and strains of swine-origin influenza viruses.


The main swine influenza viruses circulating in U.S. pigs in recent years are swine triple reassortant (tr) H1N1 influenza virus, trH3N2 virus and trH1N2 virus. Of the 25 human cases reported since 2005, 12 have been trH1N1 viruses, 12 have been trH3N2 viruses and one has been a trH1N2 virus.


All 25 persons infected with swine viruses recovered from their illness. Eighteen cases occurred in children (persons 18 or younger) and 7 cases occurred in adults. In 21 cases, direct or indirect exposure to swine prior to onset of illness has been identified.


Likely transmission of swine-origin influenza virus from close contact with an infected person has been observed in investigations of human infections with swine-origin influenza A virus, but has not resulted in sustained human-to-human transmission.

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