A WHO DON: Influenza A(H1N2)v-United States of America. Excerpt:
Situation at a glance:
On 4 August 2023, the United States International Health Regulations (IHR) National Focal Point informed PAHO/WHO of a human infection with a novel influenza A(H1N2) variant virus identified in the State of Michigan. This was confirmed by Reverse Transcription Polymerase Chain Reaction at the United States (US) Centers for Disease Control and Prevention (CDC) on August 2.
The case was not hospitalized and is recovering from the illness. Investigations by local public health officials identified swine exposure by the patient at an agricultural fair.
Additional public health response efforts including enhanced surveillance for cases is undergoing. Given the potential impact on public health, human infections with these viruses need to be monitored closely. In this event, there was no reported evidence of sustained human-to-human transmission, the illness was mild and no further influenza variant virus transmission in the community has been identified.
Description of the case:
On 4 August 2023, the United States IHR National Focal Point informed PAHO/WHO of a human infection with a novel influenza A(H1N2) variant virus identified in the State of Michigan and confirmed by the US CDC.
According to the report, the case is under 18 years old, with no comorbidities, resident in the State of Michigan, who developed respiratory illness on 29 July 2023. The case presented with fever, cough, sore throat, muscle aches, headache, shortness of breath, diarrhea, nausea, dizziness, and lethargy. On 29 July, the case sought medical care at an emergency department, and an upper respiratory tract specimen was collected on 30 July. The specimen tested positive for influenza A virus on the same day. On 1 August, the patient received influenza antiviral treatment (Oseltamivir).
On 31 July, the specimen was tested at the Michigan Department of Health and Human Services (MDHHS), and RT-PCR results were positive for influenza A virus but lacked reactivity with diagnostic tests for contemporary human influenza viruses representing either (H1) pdm09 or (H3) subtypes. The specimen was then sent to the US CDC for further testing and received on 2 August. On the same day, RT-PCR analysis of the specimen indicated an influenza A(H1N2) variant (v) virus. The virus was isolated and subsequent analysis including genetic sequencing is underway.
The case was not hospitalized. Investigation by local public health officials identified swine exposure by the patient at an agricultural fair, that took place between 23 and 29 July, within 10 days prior to illness onset. Additional investigation did not identify respiratory illness in any of the patient’s close contacts or household contacts. No additional cases were identified related to this agriculture fair. No person-to-person transmission of influenza A(H1N2)v virus associated with this case has been identified. No additional cases of human infection with A(H1N2)v virus have been identified as of 10 August 2023.
This is the first influenza A(H1N2)v virus infection identified in the United States this year. Since 2005, there have been 512 influenza A variant virus infections (all subtypes), including 37 (human infections with influenza A (H1N2)v viruses reported in the United States.
