Vital Systems Security

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

One essential point about the tiered dignostic infrastructure emerges here.  Physicians primarily have access only to the commercially available rapid tests.  This CDC website provides a list of the complicated and redundant variety of commercial tests.  Some, but not all, are able to distinguish between Influenza types A and B in addition to a basic diagnosis of influenza.  At this initial stage, influenza A diagnoses would be sent to the Public Health laboratory for subtyping with “possible further testing to occur at CDC.”

In the health alert from April 25th, the Department reports that cases from the NYC high school were identified as Type A, and were unsubtypable as H1 or H3 by the City Public Health Laboratory and were therefore sent to CDC.  At this moment, there are at least three tiers of testing: physicians can distinguish Type A or B, City health department can distinguish known influenza strains of H1 or H3, and CDC can diagnose Novel H1N1.  At this point, while they continued to advise testing with severe febrile respiratory illness of Influenza Type A, they also strongly discouraged testing of people with mild influenza-like illness.
“At this time, we are not recommending routine influenza testing and/or antiviral
treatment for persons with mild influenza-like illness, unless they meet the usual
criteria for empiric influenza treatment based on underlying illnesses that put them at higher risk for complications of any type of influenza.”

As explained in the most recent health alert, updating those reccomendations,

“At the beginning of the Novel H1N1 Influenza outbreak in late April, DOHMH initially recommended that rapid testing NOT be used for patients with mild ILI due to concerns that this newly emerging virus might lead to a severe pandemic.  This recommendation was made in order to conserve supplies of rapid test kits, and to prioritize testing for hospitalized patients with more severe disease.”
At least in the early stages, then, there was concern that commercially available rapid tests would be over-used, leading to shortages that could be critical if the outbreak increased in scale or severity.  The alert also adds more detail to the multiple tiers of diagnosis.  Again, physicans and hospitals primarily utilize commercially available rapid tests that (at best) are able to distinguish between Type A and B.  New York City’s public health laboratory utilizes RT-PCR that is able to diagnose seasonal influenza strains H1N1 and H3N2, and–by May 12, but not at the outset–confirm probable Novel H1N1.  Commercial laboratories were–as of May 12th–unable to diagnose Novel H1N1.  Viral culture diagnosis for  Novel H1N1 is only possible at CDC.

Finally, as of May 12th (the last health alert) the testing policy has been toward practices used for diagnosing and treating seasonal influenza.

“Testing for influenza is strongly recommended for:
• All patients being admitted or currently hospitalized with acute febrile respiratory illness, including
fever>100.4G F or 38.0 CG AND influenza-like illness, ARDS, pneumonia or respiratory distress.
• All patients admitted to the hospital with non-respiratory syndromes who develop acute febrile
respiratory illness > 48 hours after hospital admission.
Testing for influenza should be considered for the following patients with ILI:
• Outpatients who are at high risk for complications of influenza (see Table 2. List of underlying
conditions).
• All patients who are household contacts of persons with conditions placing them at higher risk for
complications due to influenza (including pregnancy).”

This entry was posted on Friday, May 22nd, 2009 at 3:46 pm and is filed under swine flu. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.