Day: September 9, 2019

How Good are Masks for Preventing Infection?

Patient Presentation
A teenaged female asked her pediatrician father how well masks were at preventing the spread of colds to other people. One of her friends had a respiratory illness and could not attend an important extra-curricular event and the girl was looking for possible ways to still have the friend attend. The pediatrician discussed how the friend should take care of her own health needs first and foremost. He also offered that masks can be quite helpful but they are only one part of the protective equipment used in hospitals and do have limitations including mask contamination and how the mask is actually used. It also depended on the actual illness and the type of mask used. He emphathized with his daughter and discussed other potential options for the friend to still be involved such as appropriate videochatting before and after the event.

Discussion
With continued exposure to respiratory pathogens and the emergence of novel respiratory pathogens, personal protective equipment (PPE) and procedures are important for decreasing occupational exposure to respiratory pathogens. PPE and procedures are particularly important when anti-infective treatments or vaccination are unavailable or have limited effectiveness. Medical masks are “[a]lso known as a surgical or procedure mask. As personal protective equipment, a facial mask is intended to protect caregivers and health-care workers against droplet-transmitted pathogens, or to serve as part of facial protection for patient-care activities that are likely to generate splashes or sprays of blood, body fluids, secretions or excretions. ” “N95 respirators are specifically designed to protect users from small airborne particles including aerosols…. Strict regulations dictate the filtration efficiency and breathing resistance for N95 respirators, which also require fit-testing to ensure a tight seal around the user’s face….” Mask and respirator studies are difficult to conduct because of user compliance and limited statistical power to evaluate mask and respiratory effectiveness. Therefore guidelines are based on limited evidence of their effectiveness.

Various other types of masks can be used for other protective measures such as reducing particulate matter in areas of air pollution. Other masks used for recreational and occupational activities will obviously have different effectiveness.

Learning Point
A 2017 meta-analysis designed to quantify the effectiveness of respiratory PPE among heathcare workers found:

  • In randomized controlled trials, masks and respirators had a protective effect against clinical respiratory illnesses (CRI) and influenza-like illness (ILL) when worn throughout the healthcare workers’ (HCWs) work shift.
  • Respirators offered superior protection over masks for CRI and bacterial diseases, but not viral infections or ILL.
  • In observational studies, masks and respirators provided some protection against severe acute respiratory syndrome (SARS).

There were several problems including definitions, self-report, actual mask use through the entire shift or intermittently.
The authors state that they found evidence to support using masks and respirators for CRI and ILI with respirators offering great protection to HCWs but consistent use throughout an entire work shift is less likely due to greater discomfort in using them.
In lower-resource setting they note that “….single-use medical masks are preferable to cloth masks, for which there is no evidence of protection and which might facilitate transmission of pathogens when use repeatedly without adequate sterilization.”

In a mathematical model of using PPE to reduce an influenza outbreak in a general population found that 50% compliance with using a mask or respirator resulted in a significant risk reduction, and with “an 80% compliance rate essentially eliminated the influenza outbreak.”

A study of contamination of medical masks worn by hospital HCWs found that overall contamination rate with respiratory viruses was ~10%. This increased with the duration of use, increased numbers of patients examined. They found a slightly decreased rate in pediatric and respiratory departments. Maximum contamination was found on the upper sections of the masks testing.

The authors recommend some basic practices, stating “[a]s a general rule, HCWs should not reuse masks, should restrict use to less than 6 h and avoid touching the outer surface of mask during doffing, and practice hand hygiene after removal.”

Per the World Health Organization “[w]ear medical masks fitted tightly to the face, and discard immediately after use…. If the mask gets wet or dirty with secretions, it must be changed immediately.”

The World Health Organization also states “[t]here is no evidence to suggest a difference in the effectiveness of particulate respirators over medical masks as a component in the use of PPE for routine care. However, it is not known whether there is any difference in the setting of care involving aerosol-generating procedures. When performing such procedures associated with an increased risk of transmission of [acute respiratory infections] pathogens, it may be preferable to use particulate respirators.”

Questions for Further Discussion
1. What types of PPE are available at your location and do you know how to effectively use them?
2. How contagious is tuberculosis to close contacts? A review can be found here
3. On board airplanes, where is the greatest infectious disease risk? A review can be found here

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com and the Cochrane Database of Systematic Reviews.
Information prescriptions for patients can be found at MedlinePlus for this topic: Infection Control

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Offeddu V, Yung CF, Low MSF, Tam CC. Effectiveness of Masks and Respirators Against Respiratory Infections in Healthcare Workers: A Systematic Review and Meta-Analysis. Clin Infect Dis Off Publ Infect Dis Soc Am. 2017;65(11):1934-1942. doi:10.1093/cid/cix681

Chughtai AA, Stelzer-Braid S, Rawlinson W, et al. Contamination by respiratory viruses on outer surface of medical masks used by hospital healthcare workers. BMC Infect Dis. 2019;19(1):491. doi:10.1186/s12879-019-4109-x

Yan J, Guha S, Hariharan P, Myers M. Modeling the Effectiveness of Respiratory Protective Devices in Reducing Influenza Outbreak. Risk Anal Off Publ Soc Risk Anal. 2019;39(3):647-661. doi:10.1111/risa.13181

Pacitto A, Amato F, Salmatonidis A, et al. Effectiveness of commercial face masks to reduce personal PM exposure. Sci Total Environ. 2019;650(Pt 1):1582-1590. doi:10.1016/j.scitotenv.2018.09.109

World Health Organization. Infection prevention and control of epidemic-and pandemic prone acute respiratory infections in health care. 2014. pp. xviii, pp 25-26, and Annex A2.2 pp. 40-41. https://www.who.int/csr/bioriskreduction/infection_control/publication/en/. Accessed June 24, 2019.

Author
Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa