#17,726
Last spring, in a study from the UK HSA (see UK Novel Flu Surveillance: Quantifying TTD) - officials estimated the TTD (Time To Detect) a novel H5N1 virus in the community via passive surveillance could take weeks, and the virus might only be picked up after hundreds or possibly even thousands of infections.
With avian flu beginning its fall uptick the Northern hemisphere the risk for human exposure presumably increases, prompting public health agencies to devise updated case investigation criteria and clinical management guidelines for public health officials and clinicians.
Even so, since human novel flu infection can present with a wide range of symptoms - ranging from mild or asymptomatic to severe - it is expected that some cases will go undetected.
Ten years ago, during the opening salvo of avian H7N9, researchers estimated (see Lancet: Clinical Severity Of Human H7N9 Infection) that China's surveillance was likely identifying only a tiny fraction of actual cases. Another study in the U.S. estimated that only 1 in 200 community swine flu cases were detected during an outbreak in 2011-2012.
Over the past few months we've seen a spate of updated guidance published, including:
ECDC: Targeted Surveillance to Identify Human Infections with Avian Influenza Virus during the Influenza Season 2023/24
ECDC Guidance: Enhanced Surveillance of Severe Avian Influenza Virus Infections in Hospital Settings
COCA Call: What Providers Need to Know about Zoonotic Influenza
The UK has previously released guidance for managing human infection risk in poultry workers, but yesterday they released updated clinical and exposure criteria and case management guidelines for possible community acquired avian flu infections.
For practical reasons, clinical and exposure criteria are always a compromise, using (often arbitrary) rules of thumb. In the UK:
- `Close contact' with sick, dead, or dying, poultry or wild birds is defined as < 1 meter, but we've seen anecdotal reports of people infected simply living near, or walking past an LBM (see J. Infection: Aerosolized H5N6 At A Chinese LBM (Live Bird Market)).
- A `Household contact' is defined as having more than 15 minutes, face to face contact, but there is nothing magical about the 15 minute exposure mark.
But unless you are willing and able to isolate - and PCR test - everyone who walks into a clinic or hospital, you have to set some practical parameters. While some cases will escape detection, it was never going to be a perfect net.
The link, and some excerpts from the guidance follow. Click the link to read it in its entirety. I'll have a brief postscript when you return.
Guidance
Investigation and initial clinical management of possible human cases of avian influenza with potential to cause severe human disease
Updated 17 October 2023
Before continuing with the initial assessment
Isolate the patient in a single occupancy room, preferably a respiratory isolation room and ideally under negative pressure; positive pressure rooms must not be used. Patient to minimise contact with/exposure to staff and other patients, and ask the patient to wear a surgical mask when outside the room.
Wear personal protective equipment (PPE) – as a minimum, this should be a correctly fitted FFP3 respirator, gown, gloves and eye protection.
Start oseltamivir treatment immediately if the patient meets case definition for avian influenza. For guidance on dosage refer to UKHSA guidance on the use of antiviral agents for the treatment and prophylaxis of seasonal influenza.
Case definition for possible cases
Clinical criteria
a) fever ≥ 38°C
or
b) acute respiratory symptoms (cough, hoarseness, nasal discharge or congestion, shortness of breath, sore throat, wheezing or sneezing)
or
c) other severe or life-threatening illness suggestive of an infectious process
Additionally, patients must fulfil a condition in either category 1 or 2 of the exposure criteria below.
Exposure criteria
For H7N9, H9N2, H5N1, H5N6 and any other avian influenza associated with severe human disease:
1) close contact (within 1 metre) with live, dying or dead domestic poultry or wild birds, including live bird markets, in an area of the world affected by avian influenza** or with any confirmed infected animal, in the 10 days before the onset of symptoms
or
2) in the 10 days before the onset of symptoms, close contact* with:
- a confirmed human case of avian influenza
- human case(s) of unexplained illness resulting in death from affected areas**
- human cases of severe unexplained respiratory illness from affected areas**
*This includes handling laboratory specimens from cases without appropriate precautions, or was within 1 metre distance, directly providing care, touching a case or within close vicinity of an aerosol generating procedure, from 1 day prior to symptom onset and for duration of symptoms or positive virological detection.
**For H7N9, H5N1 and H5N6 see the HCID country list. For H9N2, affected areas include China and Oman. If unsure, discuss with UKHSA Clinical and Public Health team (CPH).
Caution: Clinicians should be aware of other respiratory infections among travellers with similar presentations, such as Legionnaire’s disease or MERS-CoV, if there is an appropriate travel or potential exposure history for those infections. Consult the MERS-CoV possible case algorithm to inform assessment.
(SNIP)
(Continue . . . )
While there is always some faint hope - like in a made for TV movie-of-the-week - that swift intervention by public health officials could stop an avian flu epidemic in its tracks, in truth that's a million-to-one shot.
The reality is more likely to be like the 2009 H1N1 pandemic - where the virus was circulating quietly in Mexico for weeks or even months - before we even knew it existed. Similarly, COVID was already in Europe when countries began banning flights from China.
Early detection is still important, however. Since it allows for better treatment of initial cases, and informs officials - and the public - that the virus is in the community. Measures, such as isolating cases, the use of NPIs, and local, state, and federal responses can be started sooner, and (hopefully) the spread of the virus can be slowed.
Of course, we may get lucky, and find that H5N1 doesn't have what it takes to spark a pandemic. There may be some `species barrier' that protects us.
But even so, there is another virus out there with humanity's name on it. Developing, and implementing, procedures to detect and deal with them now is only prudent.
