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Paradigm Shift Intervention Monitoring
trH3N2 Cases to Wahington County Fair Is Tenuous
The first case of human infection with swine origin influenza A (H3) in Pennsylvania was reported in an MMWR early release issued on Friday, September 2, 2011 and occurred in a girl younger than 5 years. The two cases confirmed over the weekend also occurred in girls, both younger than 10 years. All three of the patients were in the area where swine were exhibited and one had direct contact with swine.
The above comments are from the CDC’s week 34 FluView and the September 6 “Have You Heard”, respectively, and confirm that two of the cases (both 9F) did not have contact with swine and “were in the area where swine were exhibited” which apparently just means that they lived in Washington County. The “differently enough” comment refers to the NA sequence, A/Pennsylvania/09/2011, from the younger case (2F) who was at the fair August 16, but was from Schuylkill County in eastern Pennsylvania and was symptomatic on August 20, when she present at an Emergency Department. The difference in the NA, and the presentation 4 days after attendance at the fair, raises the distinct possibility that the patient was not infected in Washington County. The two Washington County cases matched each other (A/Pennsylvania/10/2011 and A/Pennsylvania/11/2011), as well as the case (1M) in Indiana (A/Indiana/08/2011).
The dates of collections for the samples from the two Washington County cases were collected September 27 and August 25, both well outside of the time frame of the fair which began August 13 and ended August 20. Since one case was already infected September 27 (A/Pennsylvania/10/2011), she clearly was not infected at the fair. Similarly the August 25th collection date for the other Washington County case (A/Pennsylvania/11/2011) suggests that patient was infected after the fair ended.
Thus, the collection dates on the sequences deposited at GISAID by the CDC raise serious questions about the role of the fair in these cases, other than to create associations that led to trH3N2 of the symptomatic patients.
The four recent cases are very closely related to each other, except for the NA sequence from the case from Schuylkill County (A/Pennsylvania/09/2011). The dates and sequences suggest trH3N2 is widespread, but largely undetected because most samples test as seasonal H3N2. Occasionally sequences are unsubtypable, as seen in the one week 33 case, which was probably the isolate from the Schuylkill County case.
Thus, most trH3N2 cases are missed because they are not tested for trH3N2 and the number of actual cases is orders of magnitude higher than the four recently confirmed cases which had a PB1 without E618D and an M gene closely related to pandemic H1N1 isolates, with is critical for efficient human transmission.
Last season Pennsylvania reported several unsubtypable cases. These cases, as well as most H3N2 cases in Pennsylvania, should be PCR tested for trH3N2.
A realistic and comprehensive testing of these cases is long overdue.
NOTE: CDC has changed the collection date for A/Pennsylvania/10/2011 to August 26.