Study: Bird flu death rate may be overblown
February 23rd, 2012
03:57 PM ET

Study: Bird flu death rate may be overblown

The consensus among many scientists has been that the strain of bird flu currently circulating – H5N1 – is not only highly infectious, but potentially deadly. That is based on the nearly 600 cases confirmed by the World Health Organization, more than half of which have resulted in death.

But a new study analyzing WHO data suggests that H5N1 may not be as virulent as previously thought, and that mild infections could be slipping under the radar because of less-than-ideal detection methods.

Were those mild cases included, the death rate due to H5N1 could be dramatically lower, according to research appearing in the journal, Science.

"People who have evidence in their blood of prior H5N1 infection often report no history of flu-like illness," said Taia Wang, a study co-author and scientist at the Mount Sinai School of Medicine Department of Microbiology, in an email to CNN. "These cases are not identified using current WHO criteria but they are true infections and should be taken into account when calculating a fatality rate associated with H5N1 viruses."

According to Wang, strictly-defined parameters must be met to confirm an H5N1 case: a high fever, verifiable exposure to the H5N1 virus within seven days of diagnosis, and confirmation of infection by a WHO-approved laboratory.

"These criteria were designed to be extremely specific for identification of H5N1 disease, but they are not sensitive enough to identify less severe cases," said Wang.

H5N1 is lethal to certain species of birds, and in its present form, rarely infects humans. But WHO data suggest that when H5N1 does jump to humans, the potential for death is high. Of 586 people infected by H5N1 thus far, according to WHO data, 346 died.

Researchers at Mount Sinai School of Medicine analyzed 20 studies, which included 12,677 participants, but in their analysis eliminated the need for patients to show overt symptoms of H5N1 infection, as is usually prescribed by the WHO. Their analysis suggests that the rate of infection due to H5N1 could be between 1-2%.

What does that mean? According to the study, potentially, "millions of people who have been infected worldwide." If millions of people have been infected, that could dampen the impact of a mere 346 deaths.

One challenge is uniform and accurate testing, said experts. For one thing sensitive tests required to identify H5N1 are difficult to perform in rural areas where bird-to-human interaction is high (and where H5N1 is most likely to spread), so the question about the true number of cases of H5N1 is still just that - a question.

And there are issues with the tests themselves.  According to experts, current tests for H5N1 reap a lot of false-positives.

Richard Webby, director of the World Health Organization Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds, agrees that better testing is needed.

"There are almost certainly asymptomatic cases of H5N1 as there are with all influenzas," said Webby, associate member of the Infectious Diseases Department at St. Jude Children's Research Hospital, by email. "The issue is that the current [WHO] figures are based upon laboratory confirmed cases which biases this to people who are sick enough to seek medical attention."

Nathan Wolfe, author of  The Viral Storm and director of the Global Viral Forecasting Initiative, agrees that the true prevalence of H5N1 is likely higher than the cases confirmed by WHO. 

But questions linger about how much lower the mortality rate for H5N1 truly is, and what a lower rate would mean. 

"While [study authors] suggest a 'lower' mortality rate, the question is how much lower?" said Wolfe.  " The 58.6% figure [according to current WHO data] is massive so if it's really in the 20 or 30% range that's still huge."

Wolfe added that the 1918 flu pandemic was likely less than 2% mortality, so whether the mortality rate is 58.6% or it is closer to 20%, "...either way there is still plenty to fear from H5N1."

And further complicating this question are two unpublished studies, currently being held up by the journals Science and Nature, which may reveal more about H5N1's virulence.  The data are being held because of concerns it could be used for terroristic purposes.  A committee convened by WHO reported that both studies should be published in full, but did not specify when.

To get a clearer picture of how deadly the H5N1 virus truly is the next step is better testing, according to Wang.

"There is currently no organized way to detect mild or asymptomatic cases of H5N1 infection," said Wang. "The number of mild infections is important to know in order to calculate an accurate fatality rate associated with H5N1 infections."

soundoff (29 Responses)
  1. b

    The bird flu tests that were coming from Mexico were very accurate, it was a simple throat swab and RT-PCR, so you found out immediately if you were positive for it. My cousin who's an MD and responded to this crisis trained some doctors in this procedure during this crisis in Mexico to aid with efforts to counteract bird flu. I called her to diagnose myself, because my doctor did not know what to do when my lungs started caving in on me. Lucky for me I had Tamiflu at home, which is the only reason I survived. IF THERE's a new strain out, then by all means everyone, irregardless of how harmless the strain is needs to be made aware of that. The thing that my cousin worried about the most with this viral illness, was it's significant high rate of mutation. I infected my husband accidentally, but his strain was much less virulent than mine. So, while one strain may seem tamed in one individual, in another, it may be more virulent. So that needs to be addressed. This is why RT-PCR of all flu cases should be conducted in order to figure out the type, virulence, and trace mutations. This is what they do in Mexico and UNAM to follow this illness. I don't see why the US can't follow, given that our diagnostic technology is supposedly more advanced.

    February 23, 2012 at 20:38 | Report abuse | Reply
    • Elizabeth

      I have wondered for many, many years why the U.S. has made very little effort in epidemiology. There are rare exceptions such as West Nile virus, but even in that case, where is the vaccine for humans? If there are serious infections, many people also never go to the doctor because they don't want to have to sit up in a waiting room of a hospital with high fever and a cough. We are worried right now about a friend who has pneumonia but won't go to a doctor, because his city has a shortage of medical care, in the U.S. He is not only risking his life right now, but there is no way to trace who is exposed to this illness then, or what it is.

      February 25, 2012 at 23:40 | Report abuse |
    • Esteban

      i been follow this. where does you bro work and to train doc in Mexico is like wow there like really advance down there i know it dont seem that way but yeah American doc telling Mexican doc how to get a handle unlike the USA they have no issues on getting meds

      February 27, 2012 at 02:05 | Report abuse |
  2. W

    I'm all for the WHO, but swine flue anyone? After the swine flu debacle, there was no trace of acknowledgement by the WHO that this so-called epidemic had an actually lower death rate than ordinary influenza. Meanwhile, many people justified their careers while pharmas made millions in producing a redundant vaccine. If this state of affairs duplicates itself with H5N1, the WHO needs to reevaluate the way it phrases its statistical data. Alarming people may be good for jobs in science, but bad for everything else. There is actually a huge difference between 58 percent mortality and 20 percent: the difference between probably dying and probably surviving.

    February 23, 2012 at 22:49 | Report abuse | Reply
    • The_Mick

      When a kind of flu, like Swine Flu or Avian Flu is a potential next Spanish Flu (killed 50 million in 1918-19), you take precautions. Just because the new strain does not turn out to be a killer does NOT mean it was a "debacle." If you got homeowner's insurance last year and didn't have to put in a claim was it a "debacle" that you paid the premiums?

      February 24, 2012 at 04:51 | Report abuse |
    • dom625

      Of course you take some precautions, but the type of panic this sparks in some people is ridiculous. I find people strolling around in face masks unnecessary and crazy. We are going to be exposed to germs whether we like it or not.

      February 24, 2012 at 09:03 | Report abuse |
    • A scientist

      Blaming the WHO (or CDC) for the over-reaction to swine flu is a little unfair. As The_Mick points out, it is very difficult to predict when an outbreak starts how severe it is going to be. If we wait to see how the outbreak pans out before reacting, it will be too late. Therefore, it is important to prepare for the worst case scenario. If there is even a small chance that an outbreak will be like the 1918 Spanish flu (which killed millions), doesn't it make sense to prepare for this possibility? That was the case here - it wasn't that the WHO was wrong (in fact, the outbreak fell right within their predictions), it is just that the outbreak did not live up to the worst-case scenario.

      If you go back and actually read what the WHO and CDC said when the outbreak starting, they said that it was difficult to predict how severe the outbreak would be, and that it could range from something relatively minor to something as severe as the Spanish flu. Therefore, they suggested taking precautions just in case.

      It seems that a lot of people enjoy creating straw men to tear down, and pretend that the CDC and WHO was predicting certain disaster. Unfortunately, the media plays into this - they love a good story, and they can get two out of an outbreak - the first by playing up the worst case scenario (and ignoring the more cautious balanced words that scientists actually use), and the second by bashing scientist for over-stating the severity (when in fact it was the media who over-stated the severity). Of course the problem is that by over-stating each outbreak, the media is creating a cry-wolf situation, where people are less inclined to react to future outbreaks.

      February 24, 2012 at 17:16 | Report abuse |
  3. Lojolady

    Under-reacting is signlificantly more dangerous than over-reacting in the event of ANY contagious virus; all you need to do is work in a hospital for awhile and watch the rapidity with which a simple flu or "cold" spreads through a community. If a virus with severe respiratory symptoms such as severe bird flu begins to spread human to human rather than by handling dead birds, it could indeed be the next Spanish flu and millions would die. It is the under-reacting irresponsible and self-serving ones who go to work coughing and sneezing, spewing death into the environment who cause crises, not the ones who stays behind closed doors until symptoms subside. The ones strolling around in face masks are simply protecting themselves from the irresponsible ones.

    February 24, 2012 at 11:27 | Report abuse | Reply
    • Elizabeth

      I would agree, but in many cities in the U.S., going to wait in the waiting room of an E.R. for DAYS is not the best way to beat any serious respiratory illness. Patients sometimes choose what seems to be the safest route for their recovery; people do become selfish when survival is at stake. I have known people to sit up waiting for care for a very long time; more than 24 hours, in some cities. And no, they didn't go to their primary care doctor because the primary care doctor doesn't treat pneumonia.

      February 25, 2012 at 23:45 | Report abuse |
  4. Fire Girl

    This is just crazy I mean really it's just sick people. Come on doctors clam down!

    February 24, 2012 at 11:28 | Report abuse | Reply
  5. Dale

    I went to target with my friend she needed a few items, when we got through she needed to go to the ladies room as I sit there and watched people I noticed several of them were coughing and sneezing and were miserable sick, and they were spreading their germs all over the handles of the shopping carts, and then we went to the gas station I noticed the same thing people spreading germs all over the gasoline nozzles.
    ""The department of disease control should make it mandatory"" that all shopping carts are steam cleaned once a day and the same for gas pump nozzles to help stop the spread of germs.
    The American people need to start insisting upon this

    February 24, 2012 at 12:54 | Report abuse | Reply
    • Elizabeth

      At one time, before antibiotics, people used to be quarantined if they were ill. That meant they were not allowed to leave their house until they were no longer ill. These days, that is not true.

      February 25, 2012 at 23:48 | Report abuse |
  6. crown

    not the WHO or CDC but a prominent politician at the time with large stock in tamiflu to scare the world into buying

    February 24, 2012 at 20:16 | Report abuse | Reply
  7. Bazoing

    Just think of the tens if not hundreds of millions made on that little mistake.

    February 24, 2012 at 22:44 | Report abuse | Reply
  8. Elizabeth

    Two questions this article did not answer: 1. WHERE are these cases? 2. WHEN is there going to be a vaccination for this strain available in the U.S.?
    There are some serious colds this year, and should be much better reporting on epidemics.

    February 25, 2012 at 23:35 | Report abuse | Reply
    • LudicrousSpeed

      1. These cases are still mostly in people with a lot of close contact with chickens (as in the photo), as the virus does not yet readily spread person-to-person.

      2. There are stock-piled H5N1 vaccines in case H5N1 mutates to a point where it does mutate enough to be readily transmissible person-to-person, but that may not be biologically possible or the virus may not be nearly as virulent (disease causing) once it can easily spread through the human population. See the above-mentioned debate on not publishing the sequence data for that discussion.

      April 2, 2012 at 16:49 | Report abuse |
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    April 14, 2012 at 14:33 | Report abuse | Reply
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