Strategies for TB prevention
TB prevention consists of two main parts. The first part of TB prevention is to stop the transmission of TB from one adult to another. This is done through firstly, identifying people with active TB, and then curing them through the provision of drug treatment. With proper TB treatment someone with active TB disease will very quickly not be infectious and so can no longer spread the disease to others. The second main part of TB prevention is to prevent people with latent TB from developing active, and infectious, TB disease.
Anything which increases the number of infectious people, such as the presence of TB and HIV infection together, or which increases the number of people infected by each infectious person, such as ineffective treatment because of drug resistant TB, reduces the overall effect of the main TB prevention efforts. As a result it is then more likely that the number of people globally developing active TB will increase rather than decrease.
There is a vaccine for TB, but it makes only a small contribution to TB prevention, as it does little to interrupt the transmission of TB among adults.
TB prevention - the BCG vaccine
The TB vaccine called Bacillus Calmette-Guerin (BCG) was first developed in the 1920s. It is one of the most widely used of all current vaccines, and it reaches more than 80% of all new born children and infants in countries where it is part of the national childhood immunization programme.1 However, it is also one of the most variable vaccines in routine use.
The BCG vaccine has been shown to provide children with excellent protection against the disseminated forms of TB, however protection against pulmonary TB in adults is variable. Since most transmission originates from adult cases of pulmonary TB, the BCG vaccine is generally used to protect children, rather than to interrupt transmission amongst adults.
The BCG vaccine will often result in the person vaccinated having a positive result to a TB skin test
TB Treatment as TB prevention
TB drug treatment for the prevention of TB, also known as chemoprophylaxis, can reduce the risk of a first episode of active TB occurring in people either exposed to infection, or with latent TB. It can also reduce the risk of a recurrent TB episode.
For TB prevention the World Health Organisation (WHO) recommends the drug isoniazid should be taken daily for at least six months and preferably nine months.
The main "target" groups for TB treatment for prevention, are those most at risk of progressing from latent to active TB. These include:
- Infants and children aged less than 4 years old;
- People infected within the previous two years;
- People infected with both TB and HIV;
- People who have certain clinical conditions, or conditions which compromise their immune system, such as people with diabetes, and people with chronic renal failure.
Isoniazid is a cheap drug, but in a similar way to the use of the BCG vaccine, it is mainly used to protect individuals rather than to interrupt transmission between adults. This is because children rarely have infectious TB, and it is hard to administer isoniazid on a large scale to adults who do not have any symptoms. Taking isoniazid daily for six months is difficult in respect of adherence, and as a result many individuals who could benefit from the treatment, stop taking the drug before the end of the six month period.
At a Paediatric HIV/AIDS conference in Kampala, doctors were unable to agree as to whether children infected with HIV should be given Isoniazid as preventative treatment for TB. Those arguing for the drug treatment as prevention, claimed that in children co-infected with HIV and TB, up to 50% of exposed children ended up developing the disease.2
There have also been concerns about the possible impact of TB treatment for prevention programmes on the emergence of drug resistance. However, a review of the scientific evidence has now shown that there is no need for this to be a concern. The benefit of isoniazid preventative therapy for people living with HIV, and who have, or may have had latent TB, has also recently been emphasized.3
Preventing TB transmission in households
Actions to be taken
In order to reduce exposure in households where someone has infectious TB, the following actions should be taken whenever possible:
- Houses should be adequately ventilated;
- Anyone who coughs should be educated on cough etiquette and respiratory hygiene, and should follow such practice at all times;
- While smear positive, TB patients should:
- Spend as much time as possible outdoors;
- If possible, sleep alone in a separate, adequately ventilated room;
- Spend as little time as possible on public transport;
- Spend as little time as possible in places where large numbers of people gather together.
Cough etiquette and respiratory hygiene means covering your nose and mouth when coughing or sneezing. This can be done with a tissue, or if the person doesn't have a tissue they can cough or sneeze into their upper sleeve or elbow, but they should not cough or sneeze into their hands. The tissue should then be safely disposed of.4
Households where someone has culture positive MDR TB
It is not fully known how differences between drug susceptible, and drug resistant TB, as well as HIV status, affect the risk of TB transmission. However it is thought that people with drug resistant TB remain infectious for much longer, even if treatment has been started, and this may prolong the risk of transmission in the household.
In households with culture positive MDR TB patients, the following guidance should therefore be observed in addition to the measures given above.
- Culture positive MDR TB patients who cough should always practice cough etiquette (including use of masks) and respiratory hygiene when in contact with people. Ideally health service providers should wear respirators when attending patients with infectious MDR TB in enclosed spaces.;
- Ideally, family members living with HIV, or family members with strong clinical evidence of HIV infection, should not provide care for patients with culture positive MDR TB;
- Children below five years of age should spend as little time as possible in the same living spaces as culture positive MDR TB patients.
Face masks are different from respirators and can be made from either cloth or paper. A face mask worn by someone with infectious TB can help to prevent the spread of M. tuberculosis from the patient to other people. The face mask can capture large wet particles near the mouth and nose of the patient, preventing the bacteria from being released into the environment. Cloth masks can be sterilized and reused.
Respirators can protect health care workers from inhaling M. tuberculosis in certain circumstances, but they are expensive to purchase and they require specialized equipment to ensure that they fit properly. The use of a face mask does not protect health care workers against TB, and so a health care worker or other staff should not wear a face mask in a household (or indeed in a health care) setting.5
Households where someone has XDR TB
If some has culture positive XDR TB, then they should be isolated at all times, and any person in contact with a culture positive XDR TB patient should wear a particulate respirator. If at all possible, HIV positive family members, or family members with strong clinical evidence of HIV infection, should not share a household with a culture positive XDR TB patient.
Physical measures for TB prevention
A mother and her child, both with TB, at the Jessore Segregation Hospital in Bangladesh © WHO/TBP/England
Before drug treatment for TB became available, removing TB patients from their homes and putting them in isolation in sanatoria, was the main way of reducing the transmission of TB.
However this policy changed in the vast majority of countries, after studies showed that if patients stayed at home and were treated on an "outpatient" basis, this did not increase the risk of TB amongst the household contacts of the people with TB. This is because drug treatment quickly makes a TB patient uninfectious, and most household contacts who do become infected, will have already become infected before the diagnosis of TB has been made.
So generally there is now no need for people to leave their homes because they have TB. The only exceptions to this is, as described above, when someone has infectious XDR TB, and it is not feasible to isolate them at home. Also people may still need to go into a health care facility because there are complications arising from their condition, or their treatment. Within a health care facility there may be a need for some separation of people as described below, in order to reduce the chances of transmission.
The measures described above also mainly apply to resource poor settings, and the recommendations can be different where more resources are available.
TB prevention in health care facilities
Doctors and other health care workers who provide care for patients with TB, must follow infection control procedures to ensure that TB infection is not passed from one person to another. Every country should have infection control guidance which clearly needs to take into account local facilities and resources, as well as the numbers of people being provided with care. However, infection control guidance must not only be written but also implemented.
It is not just in resource poor countries that TB transmission occurs in hospitals. In 2012 it was reported that a patient in the UK had become infected with TB and had died, as a result of receiving kidney dialysis when sitting next to another patient with infectious TB.6
Major sources for TB prevention
- Implementing the WHO Stop TB Strategy: a handbook for national tuberculosis control programmes, Geneva, World Health Organization, 2008 www.who.int/tb/publications/2008/
- WHO Policy on TB Infection Control in Health Care Facilities, Congregate Settings and Households. Geneva, World Health Organization, 2009 www.who.int/tb/publications/2009/
- BCG vaccine, WHO, 2011, www.who.int/biologicals/areas/vaccines/
- Experts divided whether to give HIV positive children preventive TB treatment, NewVision, 2012 www.newvision.co.ug/news/
- Guidelines for intensified case finding and isoniazid preventative therapy for people living with HIV in resource constrained settings, Geneva, WHO, 2011 www.who.int/tb/publications/2011/
- Cover your cough, CDC, www.cdc.gov/flu/protect/covercough.htm
- Tuberculosis Infection Control in the era of expanding HIV care and treatment, Geneva, WHO, 2007 www.who.int/tb/publications/2007/
- Exclusive: patient deaths spark tuberculosis investigation, Health Service Journal, 12 October 2012 www.hsj.co.uk