#17,701
When a novel flu virus spills over sporadically into the human population it can take more than a little bit of luck for it to be picked up by passive surveillance. Most people who get flu like symptoms - even here in the United States and Europe - never see a doctor for it, and if they do, subtype testing is only rarely done.
When we see rare reports (as we did last Friday) of Swine variant infections, its a pretty good guess that far more go unreported.
A study published in 2013 (see CID Journal: Estimates Of Human Infection From H3N2v (Jul 2011-Apr 2012) - estimated that during a time when only 13 cases were reported by the CDC - that the actual number of infections was likely 200 times (or more) higher.
Results. We estimate that the median multiplier for children was 200 (90% range, 115–369) and for adults was 255 (90% range, 152–479) and that 2055 (90% range, 1187–3800) illnesses from H3N2v virus infections may have occurred from August 2011 to April 2012, suggesting that the new virus was more widespread than previously thought.The 2009 H1N1 pandemic virus is believed to have circulated, unnoticed, for several months in Mexico before being detected in April of that year, while we've seen estimates (see Lancet: Clinical Severity Of Human H7N9 Infection) that China's surveillance for avian flu may be picking up only a tiny fraction of actual cases.
More recently, a study from the UK HSA (see UK Novel Flu Surveillance: Quantifying TTD) estimated the TTD (Time To Detect) a novel H5N1 virus in the community via passive surveillance might run weeks, and might only be picked up after hundreds or even thousands of infections.
Today the ECDC has published a technical document outlining a more aggressive, risk-based targeted surveillance for avian flu, during the upcoming 2023-2024 influenza season. While some, mostly mild, cases are likely to slip through this net - by targeting specific risk groups for testing - this should reduce the TTD.
Of note, the suggested testing patients with unexplained viral encephalitis/meningoencephalitis seems a prudent move, given The Neuropathogenesis of HPAI H5Nx Viruses in Mammalian Species Including Humans.
This statement from the ECDC, followed by a link to the full 7-page Technical report.
Targeted surveillance to identify human infections with avian influenza virus during the influenza season 2023/24, EU/EEA
Monitoring
29 Sep 2023
This document describes a risk-based targeted approach to identifying possible avian influenza virus infections through established routine respiratory virus surveillance systems during the winter season 2023/24. It complements the guidance on testing and detection of zoonotic influenza virus infections in humans in the EU/EEA, and occupational safety and health measures for those exposed at work.
Executive summary
Following the autumn bird migration, avian influenza virus outbreaks are expected to occur and spread geographically across the EU/EEA. The transmission of avian influenza viruses to wild, domesticated and farmed mammals will be likely to continue. Whenever avian influenza viruses are present in wild birds and mammals, the possibility of transmission to humans cannot be excluded, particularly for those who are directly exposed while not wearing protective equipment.
During the winter months when seasonal influenza viruses are circulating in the population, testing and sub-typing approaches for avian influenza virus need to be proportionate to the epidemiological situation and the capacities of reference laboratories. Therefore, a risk-based targeted approach is proposed in areas with ongoing avian influenza outbreaks in poultry and detections in wild birds and other animals, focussing on outbreaks and severe respiratory or unexplained neurological disease.
To identify human infections with avian influenza virus, the following approach is proposed:In general, any influenza A-positive sample for which routine sub-typing using PCR has been attempted with an inconclusive result or which is negative for seasonal influenza viruses A(H1)pdm09 and A(H3), should be sent to national reference laboratories and to the WHO Collaborating Centre.
- People admitted to hospitals with respiratory symptoms should be asked about exposure to sick or dead birds, wild or other animals in the two weeks prior to symptom onset or before admission (if symptom onset date cannot be defined). They should be tested based on an exposure risk assessment by the clinician. Specimens from hospitalised patients with very severe influenza virus infections could be considered for sub-typing, particularly if they are believed to be part of a nosocomial outbreak.
- Consideration should be given to testing hospitalised patients with unexplained viral encephalitis/meningoencephalitis for seasonal influenza virus. Specimens positive for type A virus should be further sub-typed for seasonal influenza viruses to rule out avian influenza virus.
- Clusters of severe respiratory infections requiring hospitalisation should be investigated and tested for avian and other influenza viruses if routine testing for respiratory pathogens is inconclusive.
- Wastewater surveillance could be considered as an additional monitoring system locally in affected areas, however, so far there is very limited experience and evidence of wastewater surveillance being used to identify low-level circulation of zoonotic influenza virus infections in the population.
September 2023
