A sneeze in progress. Need we say more? Cover your mouth!
As we enter another influenza season, one question continues to vex medical and public health professionals: How do you stop people from catching the flu? The best way to prevent the flu is by getting an influenza vaccine every year. However, in the event of a large-scale influenza outbreak of a new virus strain or a pandemic, when influenza vaccine may not be promptly available, we will see tremendous demands on the health care system and its workers. Thus, it’s critical to understand how influenza is transmitted from person to person so that we can determine the best ways to protect health care workers while still enabling them to do their jobs.
The typical incubation period for influenza is 1-4 days (average: 2 days). Adults shed influenza virus from the day before symptoms begin through 5-10 days after illness onset. However, the amount of virus shed, and presumably infectivity, decreases rapidly by 3-5 days after onset in an experimental human infection model. Young children also might shed virus several days before illness onset, and children can be infectious for 10 or more days after onset of symptoms. Severely immunocompromised persons can shed virus for weeks or months.
Experts think influenza may be spread to uninfected people in three ways: large-particle respiratory droplet transmission, airborne transmission, and contact (or fomite) transmission. Most experts think that influenza viruses are spread mainly by large-particle respiratory droplets produced when people infected with influenza cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled. Transmission via large-particle droplets requires close contact between source and recipient persons, because droplets do not remain suspended in the air and generally travel only a short distance (usually less than 2 meters) through the air. Airborne transmission (via small particles suspended in the air for extended periods of time) also is thought to be possible, although data are limited. Less often, a person might also become infected with influenza by touching a surface or object that has influenza virus on it and then touching his or her own mouth or nose.
A better understanding of influenza transmission could help improve the infection control procedures and equipment used by health care workers. NIOSH has been conducting research for several years to learn more about the underlying science of influenza transmission, with a particular focus on airborne transmission and the protection of health care workers during a future pandemic. Here are some of the questions that are being addressed:
Is there a correlation between exposure to airborne influenza and illness among healthcare workers? A combination of three approaches is being used to better understand worker exposure to influenza and its consequences. First, aerosol sampling will be conducted in a health care clinic. Second, the amount of genetic material (RNA) from influenza virus on surgical masks, respirators and gloves worn by health care workers and on the surfaces of equipment and furniture in the clinic will be measured. Third, the health status and any occurrences of influenza among the workers in the study will be monitored. This project is part of a large multi-hospital study to compare the relative effectiveness of surgical masks and respirators in preventing influenza among health care workers.
Can better methods be developed to detect infectious airborne influenza virus? The current methods for determining the infectivity of influenza aren’t sensitive enough to work with the small amounts of virus in a typical aerosol sample. NIOSH researchers are developing new, more sensitive methods of measuring influenza virus viability. One technique is a hybrid system called a “viral replication assay” that combines PCR with a more traditional culture method for increased sensitivity. A second technique uses genetically modified cells that glow faintly when they are infected with the influenza virus. This luminescence can be detected using standard laboratory equipment.
How well do different types of personal protective equipment perform under different exposure scenarios? To explore this, NIOSH researchers constructed a simulated medical examination room containing a custom-built coughing machine that can cough an influenza-laden aerosol into the room much like a patient would, and a breathing machine that can simulate a health care worker treating the patient. The breathing machine can be outfitted with personal protective equipment (PPE), such as surgical masks, respirators, face shields, and powered air-purifying respirators (PAPRs). The simulated exam room is now being used to study how well different types of PPE and combinations of PPE protect from large spray droplets and small aerosol particles at shorter and longer distances.
Researchers at NIOSH have presented their work at scientific and public health conferences, and several articles have been published in peer-reviewed scientific journals. Information on NIOSH influenza research and influenza-related Health Hazard Evaluations can be found at http://www.cdc.gov/niosh/topics/flu/transmission.html and http://www.cdc.gov/niosh/topics/flu/hhe-projects.html. In addition, the CDC provides a comprehensive set of guidelines for preventing transmission of influenza in healthcare settings at http://www.cdc.gov/flu/professionals/infectioncontrol/healthcaresettings.htm.
William G. Lindsley, PhD
Dr. Lindsley is a Research Biomedical Engineer in the NIOSH Health Effects Laboratory Division.
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January 15, 2013 at 2:33 pm ET - Curtis Chow
I cannot find literature on PAPR vs. N-95 masks. Do you have any links? I hear of studies from the 70s or 80s
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AUTHOR COMMENT January 30, 2013 at 2:17 pm ET - William Lindsley
Thank you for your question. There were no N-95 respirators in the 1970-1980’s because this class of respirators was created when NIOSH issued new respirator regulations 42 CFR 84 in 1995. There were predecessor filtering facepiece respirators, but they would not have been classified as N95.
We have listed some articles from the 70s and 80s on the effectiveness of PAPRS below:
1. Myers WR, Peach MJ 3rd. Performance measurements on a powered air-purifying respirator made during actual field use in a silica bagging operation. Ann Occup Hyg. 1983;27(3):251-9. .
2. Lowry PL, Wheat LD, Bustos JM. Quantitative fit-test method for powered air-purifying respirators. Am Ind Hyg Assoc J. 1979 Apr;40(4):291-9.
3. Myers WR, Peach MJ 3rd, Cutright K, Iskander W. Workplace protection factor measurements on powered air-purifying respirators at a secondary lead smelter: results and discussion. Am Ind Hyg Assoc J. 1984 Oct;45(10):681-8.
4. Myers WR, Peach MJ 3rd, Allender J. Workplace protection factor measurements on powered air-purifying respirators at a secondary lead smelter–test protocol. Am Ind Hyg Assoc J. 1984 Apr;45(4):236-41.
5. Que Hee SS, Lawrence P. Inhalation exposure of lead in brass foundry workers: the evaluation of the effectiveness of a powered air-purifying respirator and engineering controls. Am Ind Hyg Assoc J. 1983 Oct;44(10):746-51.
6. Lowry PL, Wheat LD, Bustos JM. Quantitative fit-test method for powered air-purifying respirators. Am Ind Hyg Assoc J. 1979 Apr;40(4):291-9. Eneidi WL, Taylor RD. Air-purifying powered respirator pack utilizing a miniature two-stage air mover. Am Ind Hyg Assoc J. 1976 Aug;37(8):464-8.
7. Burgess WA, Reist PC. Supply rates for powered air-purifying respirators. Am Ind Hyg Assoc J. 1969 Jan-Feb;30(1):1-6.
A discussion of N-95s and Surgical masks can be found on the NIOSH blog http://blogs.cdc.gov/niosh-science-blog/2009/10/n95/ .
A more current article from 2003 may also be of interest:
Zhuang, Z., Coffey, C.C., Jensen, P.A., Campbell, D.L., Lawrence, R.B., and Myers, W.R., Correlation Between Quantitative Fit Factors and Workplace Protection Factors Measured Under Actual Workplace Environments at a Steel Foundry. American Industrial Hygiene Association Journal 64:730–738, 2003
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January 15, 2013 at 2:56 pm ET - Mike shelton
Is the flu a genetically engineered living organism?
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AUTHOR COMMENT January 18, 2013 at 2:31 pm ET - William Lindsley
No, influenza is a naturally occurring organism.
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January 18, 2013 at 5:57 pm ET - Quintin
Since the eyes are one of the routes of entry a respirator may not be an effective defense from a cough correct?
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AUTHOR COMMENT January 22, 2013 at 4:37 pm ET - William Lindsley
According to the 2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings (http://www.cdc.gov/hicpac/2007IP/2007isolationPrecautions.html) , “protection for the eyes, nose and mouth by using a mask and goggles, or face shield alone, is necessary when it is likely that there will be a splash or spray of any respiratory secretions or other body fluids as defined in Standard Precautions.” Thus, eye protection is a standard precaution that should be used in caring for any patient who creates body fluid sprays that might strike mucous membranes, including patients who create sprays of respiratory or oral secretions by coughing or sneezing.
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January 20, 2013 at 11:57 pm ET - Twitter24
Hi, just wanted to say i liked this article. it was practical. keep on posting.
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January 22, 2013 at 12:29 pm ET - Simon Lively
I’m suprised to see that there is no mention of Home / Automotive air filtration that can help keep the spread down. What about the use of UV sterilizers?
Thank you for the artical though, it was a good read.
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AUTHOR COMMENT January 30, 2013 at 9:26 am ET - William Lindsley
Thank you for your question. In its infection control guidance for influenza, CDC does not recommend use of special air handling measures in most settings, since available data indicate that influenza aerosols typically transmit infection only over relatively short distances (up to about six feet). CDC does have one exception to this policy: it recommends air filtration in health care settings where aerosol generating medical procedures are performed on patients with suspected or confirmed influenza. [See Prevention Strategies for Seasonal Influenza in Healthcare Settings at http://www.cdc.gov/flu/professionals/infectioncontrol/healthcaresettings.htm#
In the last decade, scientists and policy-makers began to examine questions around flu transmission as emergency preparedness and the emergence of the H1N1 virus stimulated further evaluation of our knowledge about infection control. NIOSH is conducting research on air filtration to help inform the ongoing dialogue in regard to potential occupational risks for health-care workers. For example, in a recent peer-reviewed paper, NIOSH researchers found that air ventilation/filtration will gradually reduce the concentration of cough-generated aerosol particles in a room; however, the risk of exposure to particles is likelier to be related to the initial concentrated bolus of aerosol from a patient, the study showed. Further study is needed to understand the implications of the findings for deliberations on infection-control policies. (WG Lindsley, WP King, RE Thewlis, JS Reynolds, K Panday, G Cao & JV Szalajda (2012). Dispersion and Exposure to a Cough-Generated Aerosol in a Simulated Medical Examination Room, Journal of Occupational and Environmental Hygiene, 9(12): 681-690, http://dx.doi.org/10.1080/15459624.2012.725986).
CDC does not recommend air sterilization with ultraviolet germicidal irradiation (UVGI) in any setting as a standard method to prevent flu transmission. Available data suggest that UV lamps must be kept far enough away from a person to prevent harmful exposure to UV radiation, and so UVGI might not be effective in preventing short-range transmission of influenza between individuals. More research is needed to better understand this and other questions about UVGI. For those interested in UVGI, more information can be found in a NIOSH document on using UVGI to combat tuberculosis http://www.cdc.gov/niosh/docs/2009-105/default.html.
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January 29, 2013 at 11:08 pm ET - gabor lantos
PAPR’s were meant to be used in industry. They were never intended nor designed for infectious particles.
How does one disinfect them? the motor? the tubing? the hood? If the healthcare worker is him/herself
infected, and asymptomatic carrier/spreader, the positive pressure from the hood will spread the infectious particles outwards towards patients! will not prevent spread as would an FFPR or half/full-face respirator.
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AUTHOR COMMENT February 14, 2013 at 9:00 am ET - William Lindsley
Thank you for your questions. The U.S. Centers for Disease Control and Prevention (CDC) provides guidance for preventing the transmission of seasonal influenza. The guidance recommends strategies for minimizing risks of transmission from an infected person to an uninfected person. Under the guidance, risks for exposure from an infected health-care worker to an uninfected patient would be minimized at the outset even before the employer makes any decisions about respirator use. As examples: If a worker is already home with the flu, CDC recommends that the employer direct the worker not to report to work. If the worker begins to show symptoms after he or she is already at work, CDC recommends that the employer direct the worker to stop patient-care activities, don a facemask, promptly notify their supervisor and the infection-control specialist at the facility, and leave work. For further information, the CDC guidance can be found at
http://www.cdc.gov/flu/professionals/infectioncontrol/healthcaresettings.htm
The CDC guidance recommends the use of facemasks for most patient-care activities and NIOSH-certified respiratory protection (which could include PAPRs) during aerosol-generating procedures, as part of a larger strategy to protect health care workers from infection. As with the use of respirators in other industries, the guidance recommends that employers follow a hierarchy of controls under which NIOSH-certified respirators would be used only after the employer has taken administrative or other steps to minimize circumstances in which respirators would be necessary. Procedures for selecting, using, and maintaining respirators in those instances for reducing work-related risks of exposure are subject to Occupational Safety and Health Administration (OSHA) requirements under 29 CFR Part 1910.134:
http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=12716
Procedures for cleaning and disinfecting respirators under the standard appear in 1910.134, Appendix B-2:
http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9782
As the blog notes, NIOSH’s research supports the advancement of work-related flu prevention by building on existing guidance, better understanding ways in which flu is transmitted, and using that knowledge to refine existing interventions and potentially develop new ones.
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January 30, 2013 at 8:40 am ET - Peter Bates
Just a short think note, “The breathing machine can be outfitted with personal protective equipment (PPE), such as surgical masks, respirators, face shields, and powered air-purifying respirators (PAPRs). ” setting up a cohort of regular urban city bus/train travelers with a filtered and unfiltered breathing machine/s to monitor virus levels for two virus events, “Adults shed influenza virus from the day before symptoms begin through 5-10 days after illness onset.” I’m sure the travellers names/contacts. etc. would be forth coming if a seat on their usual commuting conveyance was guaranteed for say, 15 working days. Further, observers placed on-board could pick their quarry quite easily once infection set in. Then just maybe, those in the cohort who did not contract the virus could be coaxed into a prospective study to find reasons for their immunity, not just from their travel to work, but their whole described environment. Maybe make a good comparative study from the semi-sterile (hospital/ clinical) environment.
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AUTHOR COMMENT January 30, 2013 at 10:11 am ET - William Lindsley
That’s an interesting idea, although the logistics would be very challenging! The breathing machine is not portable in its current design, but it might be possible to design a portable version.
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January 31, 2013 at 10:44 pm ET - Jennette Voegeli
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February 14, 2013 at 8:00 am ET - Denise Bleak RN, MSN, PHN, CIC
In acute care, efficacy of N95 respirator vs. plain isolation barrier mask protection is questionable in current flu situation: we would need to be very explicit about use, handling, disinfection. There is a significant non-work related component to influenza to consider. Hence the push to vaccinate HCW against flu: so real and so valid. Masks did not demonstrate a long term effectiveness against flu exposures, before the January surge. Our recent experience in flu surge demonstrated 18% positive rate of all patients swabbed since Jan 1, 2013 (a quick test) positive for influenza A, with 2 samples also positive for B strain, and many flu admissions. Public holding areas are positive pressure. Walk-in patients had separate holding area. Exposed, non-immune staff had no flu cases of secondary type occurred. Contrast this in January with December 2012 when during Dec 20-30 flu peaked in staff caring for inpatient flu cases; self-reported, with several people went out on leaves! (flu confers a holiday) We’ve vaccinated and asked for proof if given elsewhere-with over 60% receiving vaccine. RPP stations everywhere with tissues, signs, handwash. If ILI: droplet precautions-we say Isolate first, look for diagnosis second. Third, discharge flu cases ASAP. Vaccinate-vaccinate. Not mandatory as yet…
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