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Hospitalized H3N2v Cases Identify Community Transmission
Recombinomics Commentary 22:45
September 3, 2012

On November 19, a child aged <5 years developed acute onset of fever after 1 week of cough and congestion. The child had been hospitalized for an unrelated condition 2 days before the onset of fever.

Lake County Deputy Health Commissioner Ron Graham said a child was recently hospitalized for a short time, but recovered and is back home.

The above MMWR comment (in red) describes “patient zero” (1F) for the current H3N2v pandemic.  As noted, she was hospitalized for an unrelated condition and the initial influenza rapid test was negative.  However, a subsequent rRT-PCR test was positive and the sample was forward to the West Virginia Office of Laboratory Services (WV-OLS) confirmed the PCR test with the CDC RT-PCR test which suggested the patient was H3N2v infected.  The CDC confirmed H3N2v via sequencing (A/West Virginia/06/2011). 

The confirmation led to an epidemiological study which noted that 23 of the 70 contacts had influenza-like illness.  One sample was sent to the WV-OLS where the patient (3M) was influenza A positive (see graph), but the H3 and NP tests were negative.  However, the sample was forwarded the to CDC where partial sequences (A/West Virginia/07/2011) were obtained for 3 gene segments (HA 230/1701, NA 760/1410, MP 381/982). 

However, the partial sequence confirmed H3N2v of an isolate (A/West Virginia/07/2011) that was virtually identical to the index case.  All subsequent H3N2v cases in 2012 have matched the novel H3N2v detected in the above two patients (and was first detected in swine 3 months later).

The second comment above (in blue) describes a recent hospitalized H3N2v case from Lake County, Ohio.  Like the index case in West Virginia, the patient had no swine exposure, but the ILI hospitalization in a state with massive outbreaks of H3N2v led to testing and H3N2v confirmation.

As the H3N2v spreads, the number of hospitalized cases (currently 15 have been reported) will increase and more H3N2v cases will be identified, as acknowledged in the latest CDC update.

However, the number of cases with no swine exposure will continue to accelerate, as it becomes clearer that many or most of the H3N2v case have no swine exposure (which will be driven by outbreaks at schools), which is likely for the recently acknowleded (by sequence) H3N2v case in Kentucky and many of the 188 "seasonal" H3N2 cases reported for weeks 31-33 in the week 34 FluView.

The CDC has acknowledged community transmission in its August 31 update, but still considers these cases “sporadic” and denies "sustained" community transmission, in spite of the clear human to human clonal expansion as indicated by the 41 sets of sequences from cases across the entire county in July and August.

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