Page updated 30 April 2007
Masks for the Protection of Staff Against Tuberculosis
Introduction
Tuberculosis is more common in health care workers than to other professional groups and in the general population. Although there is anxiety about the risk to individuals caring for people with tuberculosis, the risk of catching tuberculosis from open smear-positive patients is very small indeed.
The experiments done with sentinel guinea pigs showed that there was one infectious particle in every 12,000 cubic feet of air exhausted from a ward housing men with open tuberculosis (Riley RL et al, 1962). This fits in with the average period to catching the disease in student nurses who came to look after tuberculosis cases in the days before treatment was available. The delay to getting a positive sking test or a CXR lesion was between 6 and 18 months on average.
When a patient is given anti-tuberculosis antibiotics, the risk of transmission falls day by day, because so many bacteria are killed so quickly. It seems that transmission to the close contacts of an index case is most likely to take place in the two months before the diagnosis is made. Patients are allowed out of isolation after two weeks of treatment, even though the sputum may still have viable bacteria present. This is because the perceived risk of transmission has fallen by many orders of magnitude. In the guinea pig transmission studies, there was no transmission from patients established on therapy.
The risk of disease is very low even if one is exposed. Being well-nourished and having previous immunity (usually BCG and having a positive skin test) confer protection against tuberculosis.
Nevertheless there have been cases of tuberculosis in carers of patients in outbreaks in New York particularly. There is also spread of tuberculosis between HIV-infected patients usually before the diagnosis can be made. Children and HIV-infected individuals appear particularly prone to catching tuberculosis even in an environment not considered of particularly high risk to others.
Ordinary surgical masks are very inefficient at holding up aerosol particles in the air we breathe. They cannot be recommended when nursing patients with TB. However, new efficient masks are now available which theoretically will protect the wearer against infection caused by aerosol inhalation.
One such mask, specifically designed for health care workers is "Tecnol PFR 95" and these may be ordered through your supplies department. They need to fit well to the face and will not work at all on bearded individuals. Please order a supply for your ward area if you are likely to have a patient with tuberculosis. Masks must be available for bronchoscopists, physiotherapists and morticians.
The mask should be used once only but they are quite expensive. One carer could keep their mask in their pocket for their own individual use for one shift if they are caring for one or more patients with tuberculosis.
Be careful to wash your hands after handling the mask before touching a patient because the mask will become contaminated with your mouth flora.
When to wear a Mask
We recommend the following:
- Have a high index of suspicion for tuberculosis and isolate a patient in a properly ventilated side room straight away. This is the single most important way to reduce the risk from someone with tuberculosis.
- Wea a mask if performing a risky procedure on a patient (e.g. bronchoscopy, induced sputum, tracheal aspiration in ICU or surgery). Do all these procedures in a side-room, preferably properly ventilated but, if not, at least with the window open.
- Wear a mask in the room of a patient with known or highly suspicious of multi-drug resistant (to isoniazid and rifampicin at least) tuberculosis.
- Wear a mask if you are susceptible (i.e. immunosuppressed in any way).
- Otherwise, the wearing of a mask by staff is optional.
Patients
- Patients with tuberculosis should not wear masks while outside their rooms. The masks are difficult to wear, oppressive and may make the patients feel ostracised. There is no evidence that they would reduce the risk of aerosol generation if the patient were to cough.
- Patients should wait in communal areas (X-ray, etc.) for as short a time as possible.
Visitors
- There is no need for hospital visitors who normally live with the patient to wear a mask because they will already have been exposed before admission. However, they must be examined in the local Chest Clinic (refer to the Lines of Communication for your hospital) to make sure they do not have tuberculosis. Other visitors not previously exposed to tuberculosis should be discouraged until the patient is not infectious and children should be forbidden from visiting at all.
References
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