Effect Measure

Swine flu infection of health care workers (or as CDC refers to them, health care personnel or HCP) was of interest early in the pre-pandemic phase for at last two reasons. One was the obvious goal of estimating the risk to front line workers and devising best practices for their protection. Another was the belief, reinforced by the SARS outbreak in 2003, that spread to HCP was an early warning that the virus was easily transmissible from person to person. SARS is a disease where patients are most infectious in the later stages when they are extremely ill, and HCP were among the hardest hit groups. Most flu is transmitted in the community, but the SARS model still seems appropriate for flu viruses like H5N1 (“bird flu”) where transmission is rare. Any report that a health care worker has been infected from a bird flu patient is viewed with alarm, possibly suggesting that the probability of transmission has increased. And bird flu was the template upon which pandemic planning was based. So within a few weeks of the outbreak (the first case of novel H1N1 was diagnosed in mid-April), CDC asked state health departments to report any cases of novel H1N1 among HCP. Yesterday they reported the first results in CDC’s Morbidity and Mortality Weekly Reports (MMWR):

As of May 13, CDC had received 48 reports of confirmed or probable infections with novel influenza A (H1N1) virus; of these, 26 reports included detailed case reports with information regarding risk factors that might have led to infection. Of the 26 cases, 13 (50%) HCP were deemed to have acquired infection in a health-care setting, including one instance of probable HCP to HCP transmission and 12 instances of probable or possible patient to HCP transmission. Eleven HCP had probable or possible acquisition in the community, and two had no reported exposures in either health-care or community settings. Among 11 HCP with probable or possible patient to HCP acquisition and available information on PPE [Personal Protective Equipment] use, only three reported always using either a surgical mask or an N95 respirator. (CDC, MMWR [cites omitted])

This is information from 18 states during the earliest phase of the outbreak, with illnesses that had onset between April 23 and May 4. Additional information was available for only 26 of the 48 HCP cases, so this is a small sample making generalizations risky. The HCP reporting was of special interest and not representative of all cases and we know many cases were missed in the general population. On the basis of this evidence, however, HCP don’t seem to have been a greater proportion of the cases than their percentage in the general population (“Among confirmed and probable cases in adults aged 18–64 years and reported to CDC as of May 13, approximately 4% have occurred in HCP; approximately 9% of working adults in the United States are employed in health-care settings”). In other words, infection of HCW was not a good sentinel for transmissibility in general for this virus.

What do we learn from the 26 cases with detailed information on risk factors? 50% appear to have contracted their disease in a health care setting, with at least 5 directly from a patient. In the early weeks of the outbreak hospitalizations were uncommon, so most of the HCP contracted their disease in outpatient settings. Only 3 had used a surgical or N95 mask, but of these, one, a physician used an N95 mask all the time but it had not been fit tested. In general, CDC’s recommendations for PPE during this outbreak were not followed, although masks and gloves were worn sometimes.

LLike anyone else, HCP also contracted their infections in community settings. So they are a possible vector between health care and the community in both directions. CDC emphasized in its Thursday press briefing that ongoing investigations of HPC clusters was suggesting two things related to this: (a) infectious patients should be identified as soon after they come in the door as possible so that HCP can use the necessary protective measures; and, (b) HCPs should not come to work sick. At least one of the cases was a probable HCP to HCP transmission and a sick HCP can infect vulnerable patients. We can expect to see additional guidance and better data as more data is collected and analyzed.

It is perhaps somewhat counterintuitive that HCP, with a high potential for exposure, have no higher risk. Perhaps we will revise this judgment as more reliable and larger amounts of data come available. At this point it seems that when there is lots of this virus in the community, you are as likely to get it outside of as inside a health care institution. That would seem to apply both to patients there for other reasons and to people who work there.

We’ll have to see if this holds as we learn more.

Comments

  1. #1 Snowy Owl
    June 19, 2009

    Salutations,

    Lately I have been discussing with whom it concerns about our stocks of Protective Personal Equipment (PPE) and yes medicines.

    We are in a catch 22 these days because the Fall Imported elements are not secure and dispatching a significant percentage of our stocks NOW, add stress for those who works to get what we need and what we might need in the Fall.

    One thing is sure we must now start to look at adequate alternatives in PPE and medicines for the needs of our Fall.

    Snowy

  2. #2 SARS Survivor
    June 19, 2009

    It may seem counterintuitive that health care workers are not at higher risk, but while at work, we’re conscious of infection control protocols, and tend to wear the gear and protect ourselves. But on the way home we stop for groceries and hug the kids when we get home. We’re not thinking dirty, and let our guard down.

  3. #3 revere
    June 19, 2009

    SARSsurvivor: Undoubtedly true for those with SARS history, but the data here show that infection control was not used consistently by HCP in the US and many of these were in outpatient settings.

  4. #4 SusanC
    June 19, 2009

    In London last year, Dennis Shanks from Australia presented the findings from the Australian army in 1918. Apparently, the Australian military kept detailed records of individual personnel throughout the war. So that gives an extremely useful set of longitudinal data.

    Australia was in the war much earlier than the US, and much of the data was based on personnel in the trenches of Europe, followed over several years. There were quite a few interesting findings, eg there was a inverse relationship between how long they were in the army, vs their risk of death in the second wave. In other words, new recruits were much more likely to die than those who’d been there for longer.

    The most interesting part, that bears relevance to this discussion, is that they found no difference in outcome between those who worked in different occupations in the army, with ONE exception. Healthcare personnel had LOWER mortality than any other personnel.

    It may be that we are seeing something similar here, that somehow constant exposure to, well, something, helps to protect against this virus.

  5. #5 revere
    June 19, 2009

    SusanC; Inreresting. Didn’t know the Australian data. Thanks.

  6. #6 Paul
    June 19, 2009

    Hi revere,
    Please forgive me for my question’s irrelevance to PPEs in HCPs, but it is a pressing one for me and my recommendations to my family. I’ve seen many articles in the lay press recently about the positive effects of Vit. D on the immune system’s competence, especially in actually preventing, let alone ameliorating the course of influenza infection. Recommendations seem to be up to 2,000 I.U./day,
    much higher than what is currently found in multi-vitamins (about 500 I.U.).

    I apologize for my ignorance if this is a long ago discarded recommendation, but having followed your blog for a few years, I don’t remember seeing a discussion on it – again, impugning my memory, not your thoroughness on this whole threat. Could you offer a brief comment on this, and thank you, in advance, for your tolerance.

  7. #7 Anthony
    June 19, 2009

    While we know that infected individuals weren’t using proper infection control, we don’t know that uninfected individuals weren’t, and we don’t know that more basic sanitary measures (caution about washing hands, etc) weren’t followed more reliably than in the general public. While having positive and negative risk factors completely cancel out isn’t all that probable, it’s not impossible.

  8. #8 DK
    June 19, 2009

    As a healthcare provider (NP) in an outpatient setting, I’d add some points learned so far (b/c we’re still seeing patients with H1N1):
    1. The frontline personnel-the clerks and medical assistants-have to be educated and have to buy into the protocols and the systems. It doesn’t work to have an isolation room and masks if your MA puts the patient with flu in a regular exam room w/o a mask.
    2. Planning ahead is critical. I’m a certified occupational health nursing specialist; so is the RN (at the company’s main office) who is responsible for making decisions about OSHA requirements. I repeatedly asked about fit testing for N95s, actually got in her face–and I don’t do that–only to be repeatedly told “OSHA will waive that in a pandemic”. Well, we all know that OSHA didn’t, don’t we? Idiot me, should have just gone ahead and done the fit testing.
    3. On the other hand, at least I had N95s in stock, having ordered some every now and then. How many clinics and MD’s offices would do that? I’ve got an interest in pandemic planning but it does take away from all the journal reading etc I should be doing; I’m not sure how many clinicians can keep up with everything. Speaking as someone with a huge backlog of journals…
    I could go on because we really have learned quite a lot. Unfortunately I’m worried that we’ll learn more in the fall. That’s if we can resolve one of the larger issues: we have very little “bench”–so we do come to work ill.

  9. #9 revere
    June 19, 2009

    Anthony: Alas, epidemiology isn’t about the impossible but about the likely, rejecting the unlikely. But I agree the data are highly provisional and there are many possible biases in the data. That’s why we need to wait and see. Sometimes we can make observations pending more data, sometimes not. In this case we did.

  10. #10 raven
    June 19, 2009

    Really need a vaccine ASAP. And health care workers should get it. That way if there is a major epidemic in the fall, the medical staff doesn’t have to worry as much about getting the flu. And the institutions don’t have to worry about all their staff being out sick with the flu when there is a major surge.

    The CDC had a release a few days ago. This swine flue is not behaving like seasonal flu. There are still clusters of cases long after the flu should have disappeared. They are now thinking it will linger through the summer in the Northern hemisphere and may come roaring back in the fall. Something to look forward to.

  11. #11 revere
    June 19, 2009

    Paul: First a disclaimer. I’m a physician of a certain age, which almost guarantees I learned very little about nutrition. The Vit. D issue has been swirling around flu for some years. It is a favorite among some as an explanation for seasonality. My uninformative response is that I am agnostic on Vit. D. It is a fat soluble vitamin which means it can be toxic if taken in too large amounts. It can produce high calcium and electrolyte imbalances. Will amounts in excess of current recommended daily requirements boost your immune system? I rather doubt it, but I’m not a Vit. D expert (there are many Vit. D. obsessed people out there who are also not experts). I’d make sure your family had a balanced diet and got some sunshine at the very least. That’s about as far as I feel confident in going.

  12. #12 Paul
    June 19, 2009

    Thank you, Revere, for your kind and honest response. I, too, am an older physician, but retired and mentally disabled (casualties of the profession) – may have mentioned this before (sorry if I did)- but point being, I too, learned very little about nutrition, and once entering solo practice, as one of the commenters here observed, had to be very selective in my subsequent journal reading.

    However, based upon your answer, I feel emboldened to post these two links that appear rather credible (at least to this credulous “researcher”).

    One is a very thorough discussion at Wikipedia: http://en.wikipedia.org/wiki/Vitamin_D

    The other, though dated, seems a very respectable, though anecdotal discussion, which ends in an impressive list of researchers (check their credentials at end of article) who published a paper on positive findings in *Epidemiology and Infection*: http://www.medicalnewstoday.com/articles/51913.php

  13. #13 albatross
    June 19, 2009

    This may be a dumb question, but how sure are we that this behavior of the flu virus (still circulating, albeit rather slowly, out of season) is rare? Would we have noticed this in 1990? (Or even in 2005?)

  14. #14 The Doctor
    June 19, 2009

    Today I saw a 28 y/o female with fever, cough, sore throat, nasal congestion, shortness of breath, nausea and diarrhea.

    Her symptoms began late Tuesday afternoon and became intense late last night.

    IMO, she has classic influenza and since virtually all influenza seen this summer in the US is A/(novel)H1N1, that was my diagnosis and I treated her appropriately.

    What NPI did I take? None. She was coughing in the exam room when I was there. Her husband has been extensively exposed, he is 27 y/o.

    Why didn’t I gown and mask? Well we don’t have this equipment in our office. Most doctors don’t and what the data presented above by Revere indicate that even if we did, even health care professionals who do follow NPI don’t do it well enough to prevent infection with influenza.

    So, why bother? This is why I did not gown, mask, glove, put on a face mask and don’t forget the disposable booties.

    While not a proponent of the Flu Party Fade what in essence I did today was attend one.

    I saw her today at around 10 AM. With a 2 day incubation time if I caught the virus from her this should be clear on Sunday or Monday by the latest.

    I will keep you posted.

    Grattan Woodson, MD

  15. #15 JulieRN
    June 20, 2009

    We’ve all seen the studies showing the terrible rate of compliance with handwashing protocol among doctors. It won’t be surprising if HCP infection rates increase. In my years of hospital nursing, I observed very few MDs wash their hands between patients. Interestingly enough, the female docs were much, much better about it. Many of them had been RNs before entering med school.

  16. #16 epifreek
    June 20, 2009

    Re: the Australian data, a terrific article that attempts to explain some of these findings is available at:

    http://www3.interscience.wiley.com/cgi-bin/fulltext/122456948/PDFSTART

    Mathews et al. (2009) Understanding influenza transmission, immunity and pandemic threats. Influenza and Other Respiratory
    Virus 3(4), 143–149.

  17. #17 revere
    June 20, 2009

    epifreek: Many thanks. Printing it out now. Looks good.

  18. #18 Lisa the GP
    June 21, 2009

    How are you doing, Dr. Woodson?

  19. #19 melbren
    June 21, 2009

    Me too–I wanted to check in on Dr. Woodson, as well. And the Reveres–no secondary infections so far? (Hasn’t it been about two weeks?)Wishing you all the best…

  20. #20 revere
    June 21, 2009

    melbren: Daughter still has husky voice and episodes of asthma but otherwise seems OK. Her little ones and husband seem recovered. Mrs. R. is tired and I feel like I have been hit by a a Mac truck, but otherwise OK. If you call that otherwise OK.

  21. #21 melbren
    June 21, 2009

    Revere- Feeling like you have been hit by a Mack Truck for two weeks is not OK. Does your doctor know that you still feel this badly? Maybe you have infection. (Flu-related or not.)

    And the description of your daughter mirrors that of my daughter after her “influenza-like illness,” from which she did not start perking up until she was prescribed an antibiotic.

    If your conscience bothers you about the whole herd immunity issue–just think of all that Tamiflu that the Reveres didn’t gobble up! You certainly have my vote for a “speculative” round of antibiotics!

    (You have such opinionated groupies!)

  22. #22 revere
    June 21, 2009

    melbren: Thanks for the concern. I’m quite sure I don’t have a secondary bacterial infection, but I did do 10 days of antibiotics. Flu is like this, so I’m not surprised. Plus I am working pretty hard. Too much to do. Daughter, son in law, 2 grand kids and son were here for Father’s Day and they look fine to me. So we seem to have come through this pretty typically. Not fun, but flu is flu. And yes, we do have opinionated readers. That’s what makes it fun.

  23. #23 Tom DVM
    June 21, 2009

    Great to hear everyone is fine!

    ps. I thought modern medicine was against prophylactic antibiotics

    /:0)

  24. #24 revere
    June 21, 2009

    Tom: It is. This wasn’t.

  25. #25 bubstubbler
    June 21, 2009

    Dr. Woodson,

    How do you intend to get Tamiflu into the system of a person with extensive vomiting and diarrhea?

    What do you tell your patients to do if 1) they can’t ingest it orally, 2) they can’t absorb it rectally, 3) for some reason Relenza is not a possibility, and 4) for some reason a hospital trip/stay is not a possibility?

    I understand that you’re not offering medical advice, and I won’t interpret it as such.

  26. #26 Sam Peck RN
    September 1, 2009

    It’s my understanding that swine flu symptoms are not unlike other Flu symptoms. The difference being, it attacks younger, more healthy individuals the hardest. Is this just an observation of current data coming in or has the data been compared to other Flu’s of the past? That is, on Swine flu’s effect on healthy people vs common flu’s effect on otherwise healthy people. I am 53 and have endured many a flu. The fact is, flu is a killer and I don’t feel an annual vaccine is as effective as good hygiene ie washing hands. I am not against vaccine’s, but an annual shot in the arm for the rest of my life is a different matter. I believe a STRONG push towards hygiene to be the focus, rather than a “shot” that may or may not work. Call me paranoid, But as an RN who may be forced to take a shot that “might” work, I’m left with a strong feeling of distrust!

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