May 8, 2014
News Review From Harvard Medical School -- Study Focuses on Air Flow in Spread of TB
Improving indoor air flow might help reduce the risk of spreading tuberculosis (TB), a new study suggests. The study was done in Cape Town, South Africa. TB is common and increasing in that area. Researchers measured carbon dioxide in the air of Cape Town high schools. They calculated that 1,000 parts per million of carbon dioxide indicates a high amount of rebreathed air. Researchers found that students spent almost 60% of their day in rooms with air like this. The high level of rebreathed air was caused by poor ventilation. It also showed an increased risk of spreading TB through the air. The journal PLOS ONE published the study online May 7.
By Robert H. Shmerling, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
Tuberculosis (TB) remains a terribly common and serious disease worldwide.
The World Health Organization says nearly 9 million people become ill with TB each year. Every year, 1.3 million die of the disease. More and more cases are resistant to antibiotic treatment. And the ease of travel makes the spread of TB -- including resistant strains -- a worldwide concern.
These stark facts make preventing the spread of TB a priority. A single solution may not be enough. The most important measures clearly include:
- Widespread screening
- Early diagnosis
- Prompt treatment
But there's a low-tech, non-medical approach that may not be fully appreciated: ventilation.
That's the focus of a new study. A team from Stanford University and the University of Cape Town did the research. They analyzed the air breathed by 64 students in Cape Town high schools during a school year. Their conclusions:
- Students spent about 60% of their time in an environment with a high level of rebreathed air.
- The greatest amount of rebreathed air was in classrooms with windows only on one side of the room.
- Poor ventilation could be easily addressed with low-cost changes in the classroom environment.
This study was done in an area where TB rates are high and rising. Poor ventilation may be contributing to spread of the disease.
These findings are a good example of how medical science may overlook important solutions. Diseases such as TB are often addressed with high-technology methods, such as new antibiotics or vaccines. But we may neglect low-cost, low-tech approaches such as improving the air flow in a classroom.
I recently attended a lecture about curbing the spread of TB. There was no mention of ventilation as a potential problem. There was no mention of improving ventilation as part of the solution. Yet we know, from studies of airline travelers, that ventilation can help to limit the spread of infectious illness. This new study reinforces the benefit of good ventilation. It's especially important in areas where TB is common.
What Changes Can I Make Now?
Be aware of the factors that increase the risk of TB. These include:
- Residence in an area where TB is common
- Exposure to a person known to have TB
- Impaired immune function (such as having HIV infection or taking medications that suppress the immune system)
- Alcoholism or injection drug abuse
- Organ transplantation
- Poor nutrition
- Residence in a long-term facility, such as a nursing home
- Employment in a health-care setting
Review your risk factors for TB with your doctor. Decide together whether you should have a screening test. A common screening test is a skin test that assesses your immune response to TB. More recently, blood tests have been developed. In certain circumstances, they may be more reliable than a skin test, especially if you have received a TB vaccination (called BCG).
Unfortunately, no screening test is perfect. People who have had exposure to TB may test negative (false negative results). Or test results may be abnormal even without exposure (false positive results).
Still, screening is important if you have an increased risk of TB. Many employers also require TB testing. For example, a screening test for TB is commonly recommended or required if you work in health care. That's partly because you could come into contact with infected patients. Infected health-care workers also could spread TB to others.
See your doctor if you have persistent or unexplained symptoms that could be due to active TB. Symptoms include:
- Night sweats
- Weight loss (often with poor appetite)
- Chest pain
- Swollen lymph nodes ("glands")
This new research suggests that if you live in a place where TB is common, good air flow in the classroom, at work or at home may be more important than we had known before. Talk to your local school officials or your employer if you have concerns.
What Can I Expect Looking to the Future?
I hope future studies will actually prove that improved ventilation can reduce the spread of TB. It will be important to figure out just how much fresh air is enough.
For the most part, TB remains a preventable and treatable disease. It is on the rise now in many parts of the world. But that is a failure of public health efforts. Let's hope that with more attention and resources, TB will be controlled or even wiped out in the years ahead. In places where TB is common, improved ventilation could be a good start.