I have for a while now encountered skepticism from people who believe that the number of Novel Swine-Origin H1N1 influenza cases (especially in New York and Massachussetts) is being vastly underreported by public health authorities. The claim is intriguing because of the fact that public health authorities are not testing comprehensively for H1N1, instead only testing cases of severe illness. Thus the cases of “confirmed” H1N1 may be far lower than the actual total number of cases.
How is influenza diagnosed and why isn’t every suspected case tested? First, testing for influenza is a multiple-tiered process. Tracking the NYC Department of Health “Health Alerts” over the course of the epidemic demonstrates the rationale and infrastructure behind the shifting diagnostic policies in one public health department. In the first report, from April 24th, the Department requested that physicians seeing patients in the following categories test for influenza A using a nasopharyngeal swab and a commercially available rapid test, PCR or immunofluorescence test (e.g., DFA or IFA):
(1) hospitalized patients with severe febrile respiratory illness of unknown etiology, or
(2) outpatients with influenza-like illness (ILI) who have traveled to California, Texas, or Mexico within the past 7 days
Continue reading
