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Investigation and Results

Public health and agricultural officials met with fair and 4-H club leaders and swine exhibitors and identified an initial group of eight ill persons associated with fair A. They telephoned these persons and coordinated collection of nasopharyngeal (NP) swab specimens. On September 20, seven of eight NP specimens tested presumptively positive for A(H3N2)v virus by real-time reverse transcription–polymerase chain reaction (RT-PCR) testing at MDH Laboratories Administration.

A suspected case of variant influenza was defined as influenza-like illness (ILI) (fever and cough or sore throat) among persons with swine exposure ≤7 days before symptom onset. Case-finding activities included contacting swine exhibitors through in-person meetings, telephone calls, and e-mail. Through media outreach, persons with recent swine exposure and ILI were advised to seek medical testing. MDH sent an e-mail alert to clinicians and published an Epi-X* alert call for cases. NP swabs from ill persons were collected at local health departments, clinics, and hospitals; initial testing was performed at the MDH Laboratories Administration.

On September 21, MDH was notified by the local health department of an ill person with swine exposure at fair B, and specimen collection was conducted in the patient’s home state of Delaware, in coordination with the Delaware Division of Public Health. No ill swine were detected at fair B, and no swine influenza testing was performed at this fair. The ill person had no other swine exposure and no sick contacts. On September 23, ill swine and ill persons with swine exposure at fair C were reported by fair officials. Among 294 swine at fair C, 11 were found to have fever and signs of upper respiratory tract illness. All 11 respiratory specimens collected from swine at fair C tested positive for influenza A at MDA Animal Health Laboratory and influenza A(H3N2) virus was confirmed in all specimens by NVSL. On September 27, MDH reported the first human A(H3N2)v virus presumptively positive cases associated with fairs B and C.

In total, 80 fair attendees reporting ILI were identified; 76 underwent influenza testing. Forty (52.6%) persons tested presumptively positive for influenza A(H3N2)v virus infection, including 39 Maryland residents who had NP swabs tested at the Maryland Laboratories Administration and one Delaware resident whose NP swab was tested at the Delaware Public Health Laboratory. All were confirmed to contain influenza A(H3N2)v virus by real-time RT-PCR testing and genetic sequencing analysis performed at CDC. Telephone interviews were conducted with all patients who tested presumptively positive using a novel influenza A virus case report form to collect demographic, health, and exposure information.

All patients reported attending one of three Maryland fairs (A [15], B [one], and C [24]); 52.5% were male. Patient age ranged from 9 months to 79 years; 37 (92.5%) were aged <15 years. Overall, 30 (75%) patients were at high risk for complications from influenza, including 24 aged <5 years, one aged ≥65 years, and six with a chronic medical condition. Twenty-six (65%) patients reported direct contact with swine. Fourteen (35%) patients reported only indirect contact with swine.

The median incubation period from last swine exposure to symptom onset was 2.5 days (range = 1–6 days). The most commonly reported signs and symptoms were fever (92.5%), cough (92.5%), and sore throat (40%). Eight patients reported vaccination against seasonal influenza in the past year. Two children were hospitalized; one of whom had an underlying medical condition and reported direct contact with swine. The other, admitted to an intensive care unit, was previously healthy and was wheeled in a stroller through a swine barn, but had no direct swine contact. Both recovered; there were no deaths.

Source of original article: Centers for Disease Control and Prevention (CDC) / Seasonal Flu (tools.cdc.gov).
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