Airborne Precautions

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Airborne Precautions

Introduction

Airborne precautions are procedures that are designed to reduce the chance that certain disease-causing (pathogenic) microorganisms will be transmitted through the air.

The precautions relate to airborne, microbe-containing droplets that are less than five microns in diameter (a micron is 10⁻⁶ meters). Such droplets can remain suspended in the air for a long time and so can be transported a considerable distance (such as from room to room) in even a gentle current of air. As well, particles of this size can be inhaled deeply into the lung, where the chance of establishing an infection can be increased.

Airborne precautions that involve the treatment of the air and ventilation systems are necessary for patients who have tuberculosis, and often for those with herpes zoster (shingles), varicella (chickenpox), and rubeola (measles). As of 2007, the precautions also apply to severe acute respiratory syndrome (SARS), as the mechanisms of spread of the virus are still being investigated. Other diseases do not require these mandated precautions.

History and Scientific Foundations

It has been known for over a century that some bacteria and viruses can be dispersed into the air, and that they can cause infection if they are inhaled or enter a wound. Indeed, the physical isolation of a operating theater from the rest of a hospital and the wearing of a face mask by health care providers is designed in part to limit the airborne spread of microbes.

In the United States, regulated airborne precautions were instituted by the Centers for Disease Control and Prevention (CDC). The latest guidelines were issued in 1996. The CDC also formulated separate guidelines that were specific for patients with tuberculosis.

WORDS TO KNOW

COHORT: A cohort is a group of people (or any species) sharing a common characteristic. Cohorts are identified and grouped in cohort studies to determine the frequency of diseases or the kinds of disease outcomes over time.

CONTACT PRECAUTIONS: Contact precautions are actions developed to minimize the person-to-person transfer of microorganisms by direct physical contact and indirectly by inhalation or touching a contaminated surface.

HEPA FILTER: A HEPA (high efficiency particulate air) filter is a filter that is designed to nearly totally remove airborne particles that are 0.3 microns (millionth of a meter) in diameter or larger. Such small particles can penetrate deeply into the lungs if inhaled.

Applications and Research

The airborne precautions pertain to patient placement in the hospital, transport of the patient from one area of the hospital to another, and the protective breathing gear worn by health care providers when around the patient.

According to the precautions, the affected patients must be housed in a room that has what is termed a negative air pressure relative to the surrounding spaces. Negative air pressure means that the number of air molecules in the room is less than the number of air molecules in the areas adjacent to the room. The result is that air will move into but not out of the room, reducing the chance that airborne microbes in the patient's room will disperse more widely. The air pressure of the room is monitored, the air in the room must be completely changed 6 to 12 times every hour, and the exhausted air is passed through a special type of air filter called a high-efficiency particulate (HEPA) filter that traps extremely small particles. The filter ensures that the exhausted air is not contaminated with the pathogenic microbes. The filter is changed at regular intervals and disposed of in a certain way to make sure that the trapped microbes do not pose a further hazard.

The room should also be separated from adjacent rooms and hallways by a door, which is left closed when not in use.

Ideally, the room should be just for the affected patient. If this is not possible, then more than one patient can be housed in the same room (this is called cohorting). These cohorts should have the same infection that is caused by the same microorganism (there are exceptions for tuberculosis). However, the patients should not have any other infections. If these precautions cannot be met, then another strategy should not be undertaken without the advice of infection control experts.

The precaution concerning respiratory protection is specific. When entering the affected patient's room, health care providers must wear an N-95 respirator, which is a mask certified by CDC's National Institute for Occupational Safety and Health (NIOSH). The mask is equipped with a filter that can trap over 95% of particles that are 0.3 microns or greater in diameter in an aerosol that is free of oil (oil can affect droplet size and is not the sort of aerosol encountered in hospitals).

Anyone who is susceptible to rubeola or chickenpox should not enter the room of a patient with these diseases without an N-95 mask. A person who has a compromised immune system should not have close contact with a person whose illness requires airborne precautions. This applies to other patients as well as visitors and health care personnel.

Airborne precautions also pertain to the movement of patients within the hospital. This movement should only be done when absolutely necessary. During transport, a surgical mask is placed over the patient's nose and mouth to minimize the dispersal of droplets.

Impacts and Issues

Airborne precautions reduce the spread of certain infections. But this safeguard comes with a price tag. Equipping hospital rooms to be negative pressure rooms, installing and maintaining HEPA filters, and equipping staff with respirators is expensive. Furthermore, the requirements to frequently document compliance with the precautions is an added burden to hospital caretakers.

One recent example highlighting airborne precautions concerns a type of recently emergent Mycobacterium tuberculosis that is extremely resistant to antibiotics. According to the World Health Organization (WHO), the extreme drug-resistant tuberculosis (XDR-TB) is virtually untreatable using the present arsenal of drugs. Strains of XDR-TB have been noted in individuals mainly in South Africa, but also in Russia, North America, South America, and Asia. According to WHO, people infected with the human immunodeficiency virus (HIV) are particularly susceptible to XDR-TB. As of 2007, prevention and containment through the use of airborne precautions constitute the main line of defense against XDR-TB.

IN CONTEXT: AVAILABILITY OF HOSPITAL BEDS

Airborne precautions pertain to patient placement in the hospital, transport of the patient from one area of the hospital to another, and the protective gear worn by health care providers when around the patient.

But how available are the hospital beds?

The list below reflects selected data from the World Health Organization that demonstrates the wide disparity in results reported by WHO as of February 2007. Data was not available for all countries, including a lack of data for: Angola, Botswana, Burkina Faso, Central African Republic, Chad, Ethiopia, Ghana, Kenya, Mali, Niger, Rwanda, Senegal, Togo, Uganda, and South Africa.

Country; Hospital beds (per 10,000 people); (Year data gathered).

Nepal 1.5 beds (2001)
Bangladesh 3.4 beds (2001)
Afghanistan 3.9 beds (2001)
Somalia 4.2 beds (1997)
Guatemala 5 beds (2003)
Cambodia 5.72 beds (2004)
India 6.9 beds (1998)
Sudan 7.1 beds (2003)
Haiti 8 beds (2000)
Mexico 10 beds (2003)
Philippines 11.45 beds (2002)
Iran (Islamic Republic of) 16.3 beds (2001)
Egypt 21.7 beds (2003)
Thailand 22.3 beds (1999)
Maldives 22.6 beds (2003)
Viet Nam 22.8 beds (2003)
China 23.11 beds (2004)
Sweden 30 beds (2004)
United States 33 beds (2003)
Ireland 35 beds (2004)
Canada 36 beds (2003)
United Kingdom 40 beds (2003)
Italy 41 beds (2003)
Cuba 49 beds (2004)
Switzerland 59 beds (2003)
France 76 beds (2003)
Russian Federation 99 beds (2004)
Belarus 107 beds (2004)
Japan 129.37 beds (2001)
Monaco 196 beds (1995)

SOURCE: WHOSIS (WHO Statistical Information System), World Health Organization, Regional Office websites and publications.

BIBLIOGRAPHY

Books

Lawrence, Jean and Dee May. Infection Control in the Community. New York: Churchill Livingstone, 2003.

Tierno, Philip M. The Secret Life of Germs: What They Are, Why We Need Them, and How We Can Protect Ourselves Against Them. New York: Atria, 2004.

Periodicals

Booth, Timothy F., et al. “Detection of Airborne Severe Acute Respiratory Syndrome (SARS) Cornonavirus and Environmental Contamination in SARS Outbreak Units.” Journal of Infectious Diseases 191 (2005): 1472–1477.

Yu, Ignatius T.S., Tze Wai Wong, Yuk Lan Chiu, Nelson Lee, Yuguo Li. “Temproal-spation Analysis of Severe Acute Respiratory Syndrome among Hospital Inpatients.” Clinical Infectious Diseases 40 (2005): 1237–1243.

Brian Hoyle

Infectious Diseases: In Context