Tuberculosis

4904528874_882a5d1019_oThe state of your home can have a direct impact on the state of your health. And if your home has poor ventilation, a lot of dampness, or even mold, your susceptibility to an infectious disease such as tuberculosis (TB) is heightened.

TB, an airborne infectious disease caused by the bacterium Mycobacterium tuberculosis, most commonly affects the lungs. Currently there are approximately 2 billion people—one-third of the world’s population—who are infected with TB; an estimated 1.4 million people died from TB in 2011 (WHO). The majority of TB deaths occur in the developing world, and the disease is also a leading killer of young adults worldwide. When a person with an active TB infection coughs, sneezes, or spits, TB bacteria are released into the air; from there they can be inhaled by uninfected individuals, thereby giving the disease a chance to spread. If the bacteria linger in the air, which is often the case in homes with high humidity and little air movement, the likelihood of infection greatly increases. Left untreated, each person with active TB disease will infect between 10 and 15 people every year (WHO).

Drug-resistant forms of TB further complicate the picture. The standard treatment regimen for TB is complicated and usually lasts 6 months, but improper or inconsistent treatment can lead to the development of drug-resistant TB strains. Multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) have both developed as a result of incorrect anti-TB drug usage; these forms of TB are difficult and expensive to treat, as they fail to respond to standard first-line medicines. Preventing new infections, therefore, is of paramount importance. There were an estimated 500,000 new MDR-TB cases worldwide in 2011 (WHO). Inadequate ventilation has been shown to be a contributing factor in the growth of MDR-TB infections.

Certain populations are more susceptible to developing TB infections. People who are infected with HIV have weaker immune systems; this increases the likelihood of both TB infection and the risk that such infection turns into active TB. The risk of developing active TB is estimated to be between 20 to 37 times greater in people living with HIV than among those without HIV infection, and approximately 430,000 people died from HIV-associated TB in 2011 (WHO). This type of HIV-TB co-infection is found among many who are homeless, but homelessness itself, separate from HIV status, also presents an increased risk of developing TB. In many industrialized countries, TB rates among the homeless can be up to 20 times higher than those of the general population (WHO). Particularly in the winter, when housing facilities are more likely to be crowded and inadequately ventilated, shelters and rooming houses can facilitate rather than reduce TB transmission (Harmony House, 2008).

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Housing, then, has an important role to play in stemming the spread of the disease. Good ventilation is the most important way to prevent TB transmission regardless of the type of housing environment (NIAID, 2012). Factors such as occupancy density, room volume, and air change rate are directly correlated with the number of new TB infections among persons who share airspace. And the presence of mold and fungi in homes is associated with suppressed T-cell production, which has been linked to slower recovery from TB. The threat of new TB infections can be reduced 75% by controlling the airborne capacity of TB-infected aerosol through adjustments to relative indoor humidity and ventilation flow rates.

ARCHIVE Global is currently building houses in Saint-Marc, Haiti, to help reduce the incidence of TB there. Constructed with mostly local materials, these houses use stacked ventilation with perforated walls to maintain continuous airflow. The houses also have less indoor humidity and better access to sunlight. ARCHIVE seeks to improve health outcomes in Haiti through a combination of construction and community education, and it is our hope that we can contribute our knowledge of housing design to the global fight against TB.