CIDRAP News Headlines (Septembre 2006)

[Nancy]

http://www.cidrap.umn.edu/cidrap/content/influenza/avianflu/news/sep0706cambodia.html

Cambodian study suggests mild H5N1 cases are rare

Sep 7, 2006 (CIDRAP News) ? Researchers who tested 351 Cambodian villagers after they had extensive contact with avian influenza?infected poultry in 2005 found that none had antibodies to the H5N1 virus, suggesting that it doesn't easily spread to humans and that mild cases are rare.

"Our findings suggest that asymptomatic and mild H5N1 virus infections had not occurred in the population we investigated," says the report, published by Emerging Infectious Diseases. The study was done by an international team of scientists, with Sirenda Vong of the Institute Pasteur in Phnom Penh, Cambodia, as first author. Preliminary results were reported at a conference last March.

Some experts have speculated that the current case-fatality rate for H5N1 avian flu, about 59%, could be inaccurate because mild or asymptomatic cases have gone undetected. Few such cases have been found in the limited number of studies on the topic so far.

The village involved in the new study was the home of a 28-year-old man who had Cambodia's second confirmed H5N1 case. The man, from Banteay Meas district in southeastern Cambodia, died in March 2005.

After his death, Cambodian health officials launched an investigation to find additional cases and identify how the patient was exposed. The researchers said the rural village setting allowed them to study the epidemiologic features of the H5N1 virus in poultry and humans. Focusing on a 1-kilometer radius around the patient's house, the researchers conducted a retrospective survey of poultry deaths immediately after the patient's H5N1 infection was confirmed. Two months later they conducted a serologic investigation of members of 93 households.

Villagers were questioned about recent illnesses in their chickens, and researchers collected samples from sick, dead, and randomly selected healthy chickens. The investigators also interviewed villagers about their exposure to animals and the environment during the previous 12 months and took blood specimens from each of them.

The poultry survey revealed that 42 households were likely to have had an outbreak of H5N1 in poultry, reflecting an overall attack rate of 27% among households with chickens. Only two households reported the simultaneous deaths of ducks, and raising ducks with chickens was not associated with deaths in chickens.

Cloacal specimens from two sick chickens tested positive for the H5N1 virus. The owner of the chickens reported that the man who died of avian flu had spent daylight hours in his compound.

In the serologic survey, investigators found that substantial numbers of villagers had had regular, close contact with poultry or pigs over the previous 12 months. Despite this, none of the villagers reported having had a febrile or respiratory illness during the same period, and none of the residents had antibodies that suggested they had been infected with the H5N1 virus.

The researchers said their finding of little H5N1 transmission between infected poultry and humans is consistent with recent studies among healthcare workers and household contacts of patients. The findings also suggest that none of the villages had an asymptomatic or mild H5N1 infection, they added.

The authors said they couldn't explain why only one person became infected when so many others had similar exposure and did not have evidence of infection. "H5N1 virus transmission in humans may be rare because it only occurs in exposed persons with unique host susceptibilities and a predisposition to an abnormal inflammatory response that results in severe and fatal outcomes, rather than causing a broad spectrum of illness with mild disease and subclinical infections," the article states.

The scientists found that some poultry-keeping practices appeared to affect a flock's chance of contracting the H5N1 virus. Handling poultry, cleaning their stalls and cages, and collecting feathers seemed to reduce infections, while purchasing live poultry seemed to increase the risk.

Though the H5N1 virus does not spread easily to humans, the researchers cautioned that that could change as the virus continues to circulate and evolve, and they called for routine, extensive investigations of all H5N1 outbreaks among humans and animals.

Vong S, Coghlan B, Mardy S, et al. Low frequency of poultry-to-human H5N1 virus transmission, southern Cambodia, 2005. Emerg Infect Dis 2005;12(10) [Full text]

See also:

Mar 27, 2006, CIDRAP News story "Mild H5N1 cases weren't missed in Cambodian outbreak"

Mar 29, 2005, WHO statement on second Cambodian case

http://www.who.int/csr/don/2005_03_29b/en/index.html

Sep 29, 2005, New England Journal of Medicine article "Avian influenza A(H5N1) infection in humans" (see table 2 for results of serologic testing of patient contacts) [Full text]

[Mellie]

Re: CIDRAP News Headlines (Septembre 2006)

http://www.cidrap.umn.edu/cidrap/con...6airborne.html
Airborne flu viruses threaten health workers, expert says

Robert Roos News Editor

Sep 29, 2006 (CIDRAP News) ? A microbiologist who reviewed the evidence about how influenza viruses spread says that some official guidelines, including the US pandemic influenza plan, may not go far enough in protecting healthcare workers who take care of flu patients.

Writing in Emerging Infectious Diseases, Dr. Raymond Tellier of the University of Toronto says there is good evidence that flu viruses often spread via tiny airborne particles, despite a common belief that they travel mainly in large droplets that quickly fall to the ground after a flu patient coughs or sneezes.

Good protection from airborne particles requires the use of an N95 respirator. Yet the US, Canadian, and British pandemic flu plans advise healthcare workers to use simple surgical masks, which are much less effective, Tellier contends.

"Compelling evidence in the literature indicates that aerosol transmission of influenza is an important mode of transmission, which has obvious implications for pandemic influenza planning, and in particular for recommendations about the use of N95 respirators as part of personal protective equipment," he writes.

"Airborne particles" are usually defined as particles about 5 microns or less in diameter, Tellier says. Particles larger than about 10 to 20 microns fall quickly to the ground, while those smaller than 3 microns essentially do not settle. Coughing and sneezing generate particles in a range of sizes, many of them small enough to stay airborne for a long time. Airborne particles can penetrate into the lungs, whereas the larger particles and droplets are more likely to be trapped in the upper respiratory tract.

Experiments have shown that mice, monkeys, and human volunteers can be infected by exposure to aeorosol flu viruses, according to Tellier. In addition, various epidemiologic observations indicate that aerosol transmission is important. One example was a 1979 outbreak on an airliner with a defective ventilation system.

Tellier says many guidelines and review articles state that large droplets appear to be the main vehicle for flu virus transmission, but they offer little supporting evidence. "Despite extensive searches, I have not found a study that proves the notion that large-droplets transmission is predominant and that aerosol transmission is negligible (or nonexistent)," he writes.

Further, he says, infection control experts often argue that large-droplet precautions have proved adequate to stop flu outbreaks. But he contends that several factors cast doubt on the evidence for this view. For example, without laboratory diagnosis, what is believed to be a flu outbreak can be some other virus; serologic studies often are omitted, and asymptomatic flu infections in healthcare workers are probably missed; many people have partial immunity to seasonal flu viruses; and surgical masks provide some limited protection against aerosols.

Tellier goes on to say that evidence suggests that current strains of H5N1 avian influenza predominantly infect the lower respiratory tract, which in turn suggests that airborne particles are involved, since large droplets don't reach into the lungs.

"Given the strong evidence for aerosol transmission of influenza viruses in general, and the high lethality of the current strains of avian influenza A (H5N1), recommending the use of N95 respirators, not surgical masks, as part of the protective equipment seems rational," he states.

The current US pandemic influenza plan, according to Tellier, "acknowledges the contribution of aerosols in influenza but curiously recommends surgical masks for routine care; the use of N95 respirators is reserved for 'aerosolizing procedures.'"

In contrast, the Centers for Disease Control and Prevention's (CDC's) current infection control guidelines for healthcare facilities treating avian flu patients say that workers should use a fit-tested respirator at least as good as the N95 type when in a patient's room.

Bill Hall, a Department of Health and Human Services (HHS) spokesman in Washington, said today that the infection control guidance in the US pandemic flu plan is being updated. "We are conducting a rather in-depth process by which we'll be reviewing the science that is available on masks and the various positions out there," he told CIDDRAP News. "This journal article certainly adds one more data source to inform the decision-making."
"There's still a lot of debate on how flu is transmitted, whether it's aerosol or large droplets," Hall said. "The [pandemic] plan issued in November last year was based on current science and information at that point in time," but it is subject to change, he added.

Hall said HHS plans to cooperate with the Institute of Medicine to hold some workshops to discuss "community mitigation" in a pandemic, meaning measures such as closing schools, canceling public events, and recommending the use of masks. But no dates or other details have been decided.

Tellier R. Review of aerosol transmission of influenza A virus. Emerg Infect Dis 2006 Nov;12(11) (early online publication) [Full text]

See also:
CDC interim guidance on use of masks to control influenza
http://www.cdc.gov/flu/professionals...skguidance.htm

CDC interim infection control guidelines for healthcare facilities treating people with avian flu
http://www.cdc.gov/flu/avian/profess...ct-control.htm

[sharon sanders]

Re: CIDRAP News Headlines (Septembre 2006)

bump this

[AlaskaDenise]

Re: CIDRAP News Headlines (Septembre 2006)

The above article is an interesting discussion of something we haven't talked about for months - droplet size implications.

If US pandemic plans recommend N95 masks only "for 'aerosolizing procedures'", yet influenza is being spread by aerosol despite living in deep lung areas, then HCW should be following the CDC recommendations - "workers should use a fit-tested respirator at least as good as the N95 type when in a patient's room."

I'm glad this article clarifies the conflict in the plans - were I a HCW, I'd be following CDC recommendations.

How many hospitals have sufficient supplies of these respirators? Do they come with easily-replaceable filters?

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