September 23, 2009
H1N1 2009: For the most recent reporting week, the CDC again documented an
increased number of confirmed cases of infection due to H1N1, including
two pediatric deaths. There are now 21 states with widespread disease
reported, but even in those states disease occurrence is not uniformly
distributed. We continue to see positive cases both by rapid diagnostic
tests and PCR. For each of the last three weeks, we have seen a steady
increase in the number of tests submitted for analysis as well as the
number of positives. As of today, about half of our requests for testing
are internal (ED, UCC, CHC, pulmonary) and the other half are from the
offices of community physicians.
We have received a number of questions about the sensitivity and
specificity of the various testing kits that are commercially available.
The CDC reported data in August on the ability of three kits to detect
influenza isolates in general and novel H1N1 more specifically. In the
case of the H1N1 isolates, the numbers are small. For the three kits
(BinaxNOW, Directigen EZ Flu and QuickVue A+B), the sensitivity for all
flu isolates was 51%, 58% and 72%, while for H1N1, it was 40%, 49% and
69%. Investigators from Atlanta reported on four kits, looking at all
isolates not just H1N1, and concluded that the sensitivity was 88-96% for
Directigen, 62-88% for Flu OIA, 73-81% for QuickVue and 57-65% for
ZstatFlu. There is significant variation in the sensitivity of the tests,
as well as some concern over specificity values of 93%, which means that
false positives are also an issue.
In a recent publication, the CDC says that in the event that a rapid test
is negative for Flu A and B, the clinician “should use clinical symptoms,
severity and underlying disease to decide if antiviral treatment is
appropriate, should not use a negative rapid test to send a symptomatic
child back to school, to rule out an institutional outbreak or to dictate
infection control practices, should consider whether additional testing is
needed by using viral culture and rRT-PCR and should consider whether
additional diagnostic testing and/or empiric antibiotic therapy for
co-infections is indicated”.
H1N1 VACCINE AVAILABILTY: On Friday, the CDC released more information on
the availability and distribution of the novel H1N1 vaccine. There are
five manufacturers producing vaccine for the US. The first vaccine is
expected to be shipped by mid-October, with the possible availability of
some vaccine by late September. Vaccine will be shipped to clinics,
offices, health departments and other project area-designated sites. The
vaccine will be purchased by the federal government. Charges for
administration fees will be allowed. Vaccine will be allocated based upon
population. One dose of vaccine will be sufficient for persons aged 10
years and older. Dosing schedule for children is not yet known. Seasonal
and novel H1N1 can be given at the same time (except seasonal live vaccine
and live H1N1 should not be combined). There will be a separate allocation
for Department of Defense personnel, but not for dependents, retirees and
civilian employees. Recommendations for vaccine include pregnant women,
people who live with or care for children under 6 months of age, health
care and emergency medical services personnel, persons between the ages of
6 months and 24 years of age, and people from 25 years of age to 64 years
of age with chronic medical conditions. It may be necessary to prioritize
further within these groups based upon vaccine availability. Stay tuned
for more details.
CME online
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