Tall and thin women at risk of certain type of lung infection

"Nontuberculous mycobacteria are widespread in the environment, yet only some people develop infections," said Edward Chan, senior author and professor of medicine at National Jewish Health in US.

"These findings help us identify who is at greater risk for the disease, and may point to more effective therapies down the road," Chan said.

Although the organisms can infect skin and other body parts, they most commonly infect the lungs. Lung infections are very difficult to treat, often requiring surgery and years of therapy with powerful intravenous antibiotics.

NTM species are widespread in water and soil, yet only about five to six people per 100,000 develop NTM infections each year; the incidence is higher in individuals older than 50 in the US.

An estimated 30,000 to 120,000 people in the US currently have NTM infections.

Researchers at National Jewish Health, which sees more NTM infections than any other medical center in the world, tried to figure out why only some exposed patients develop these difficult infections.

Elderly women represent the vast majority of NTM patients, accounting for 85 per cent of the patients seen at National Jewish Health during the study, and averaging about 64 years of age.

Researchers compared the NTM patients with control subjects at an osteoporosis clinic because these individuals were similar age, race, and gender as the NTM patients.

When compared to the women visiting the osteoporosis clinic, the NTM patients were on average almost two inches taller, had body mass indices almost two points lower and 5.7 pounds less fat on their bodies.

The NTM patients also more frequently had concave chests, a condition known as pectus excavatum, and scoliosis, or curvature of the spine.

"Tall, thin women definitely appear to be more susceptible to NTM infections," said Chan.

"They share some characteristics of people with Marfan syndrome. Since Marfan syndrome is caused by a mutation in the fibrillin-1 gene, we plan to look at that gene as a potential source of NTM susceptibility," Chan said in a statement.

Marfan syndrome is a disorder of connective tissue, the tissue that strengthens the body's structures. People with Marfan tend to be unusually tall, with long limbs and long, thin fingers.

Women with NTM infections also showed a weakened immune response associated with their fat cells.

The study was published in The American Journal of Respiratory and Critical Care.