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trH3N2 Cases In Indiana and Pennsylvania Match
The above data is from today’s MMWR (week34), which cites two new trH3N2 infections in Pennsylvania and Indiana. The listing of two trH3N2 for the current week is without precedent. Prior cases (A/Kansas/13/2009, A/Iowa/16/2009, A/Minnesota/09/2010, A/Pennsylvania/40/2010, A/Wisconsin/12/2010, A/Pennsylvania/14/2010, A/Minnesota/11/2010, and A/Indiana/08/2011), were reported after the fact, and in many cases the reporting was months after the fact.
Two of the cases (WI/12/10 and PA/14/10) were announced in a WHO pager alert, which generated alarm in Europe. However, the WHO noted that the cases were isolated 6 weeks apart and the sequences were distinct and not from a common source and therefore the trH3N2 was not transmitting. However, PA/40/10 was from a patient infected within a week of WI/12/10 and the sequences were virtually identical, but PA/40/10 was not reported until 2011 and the close identity was not noted by the CDC. Thus, when the alert was announced there really were three cases (two in September and one in October) and the two September cases raised transmission concerns.
These concerns were increased when MN/11/10 was announced. The sequences from the November case was closely related to WI/12 and PA/40, and contacts of MN/11 were under investigation. In 2011 the daughter of the MN index case was H3N2 confirmed, and her lack of swine contact indicated she was infected by her father. Moreover, additional family members had been symptomatic, indicating MN/11 had spread. Concern regarding this spread increased when the CDC deposited sequencing indicating MN/11 had been selected as a vaccine target.
Concern was increased further when a new case was announced in the week 30 MMWR. That announcement was followed by the release of a set of sequences from Indiana, which was a reassortant that had acquired a pandemic H1N1 MP gene segment. Moreover, this isolate had an H3 that was closely related to the sequences from MN, PA, and WI raising concerns that this H3 was adapting to humans.
In spite of increased swine surveillance, which included release of HA sequences, most of the H3 sequences closely related to IN/08/11 were human trH3N2 isolates, and today’s MMWR cites another Indiana case as well as another Pennsylvania case.
Although the spike in cases in the past month is of more concern that the two cases cited in the 2010 pager alert, WHO and the CDC have not commented on these cases, or the selection of MN/11 as a pandemic vaccine target.
The relationship between the Indiana cases is unknown, which is also true for the recent Pennsylvania case.
More information on these cases is overdue.
BREAKING: Media reports indicate the two recent cases are children infected with trH3N2 with H1N1 MP.