Each year, more and more people are getting mycobacterial lung infections, and the total number living with such diseases is going up, according to a new study published in the journal Annals of the American Thoracic Society. Those at greatest risk are people above the age of 65 years and the elderly.
Mycobacteria are best known for the strains causing leprosy and tuberculosis. However, there are other mycobacteria that do not cause tuberculosis but do cause lung infections, and these are called non-tuberculous mycobacteria (NTM). These are part of the natural environment and are inhaled by most people. Among these, Mycobacterium avium complex is the most commonly found, but there are over 160 different species of them.
Mycobacterium avium-intracellulare, MAI, non-tuberculous mycrobacteria which cause opportunistic infections in HIV-infected patients, 3D illustration Credit: Kateryna Kon / Shutterstock
NTM lung disease
NTM causes sickness in a very small percentage of those who inhale them. However, people with chronic lung conditions such as chronic obstructive pulmonary disease, emphysema, bronchiectasis and cystic fibrosis are at greater risk. So are those with weak immune systems have a higher risk of NTM-caused lung disease. When this occurs, it can be severe and even deadly, but rarely spreads from person to person.
The clinical features of NTM lung disease include a chronic cough with sputum, fatigue, fever, bringing up blood on coughing at later stages, and unintentional weight loss. It is diagnosed based on the clinical evidence and the tests showing that NTM infection is active in the patient, such as seeing NTM in the sputum, culturing sputum to try and grow NTM (though this may take weeks in some cases), and sometimes bronchoscopy to take samples.
Once diagnosed, three or more antibiotics are given until the sputum culture turns out negative for 12 months. These drugs may be toxic and careful follow up is required. Other supportive treatment may be required depending on the patient’s condition.
The investigators looked at 27 million participants in a large national-level healthcare plan (Optum) over a period of 8 years (2008 to 2015). They analyzed their healthcare records to find the incidence of NTM infections, which means the number of new infections that are reported each year per 100,00 person-years. One-person year is exactly what it sounds like, one year of life per person included in a statistic. They also found the prevalence, which is the total number of people living with NTM per 100,000 people.
Within the study period, they found that the incidence of lung disease caused by NTM each year went up from 3.1 to 4.7 per 100,000 person-years. The prevalence per year went up from 6.8 to 11.7 per 100,000 persons. Both incidence and prevalence rose by at least 10% in 29 states in the US over this period.
The annual incidence was higher for women at the beginning of the study, at 4.2, and went up to 6.7 at the end. The annual prevalence in women also increased from 9.6 to 16.8. In people aged 65 years and above, the annual incidence went up from 12.7 to 18.4, and the annual prevalence went up from 30.3 to 47.5.
Researcher Kevin Winthrop cites many reasons for this rising trend, and the disproportionate increase in certain groups, saying, “The number of people at risk is increasing because the population is aging and more people are living with chronic lung diseases. Increasing environmental exposure is also likely a factor, as is greater awareness of NTM disease among physicians.”
Since NTM is known to affect the elderly, with their age-weakened bodies and slower immune responses, women, who typically live longer than men, are more likely to be affected. Moreover, women may be more likely to seek medical advice, leading to higher rates of diagnosis.
The rising numbers of people with chronic lung disease due to smoking and other lifestyle choices, pollution, and allergic asthma, as well as their longer survival with current medical treatment, predisposes to a greater prevalence of NTM which typically targets this group.
Doctors have also become more alert to the possibilities of NTM among their patients, and this may increase the rates of diagnosis. Other factors as yet unknown could include biologic and genetic factors that make women more susceptible to this condition.
The researchers listed the limitations of their work, such as their reliance on diagnostic codes in the health records which could be incorrect due to coding inertia, or the nonavailability ofexact codes; and the possible lack of national representation as the number of participants in this health plan varied significantly across the country.
Incidence and Prevalence of Nontuberculous Mycobacterial Lung Disease in a Large United States Managed Care Health Plan, 2008-2015. Winthrop KL, Marras TK, Adjemian J, Zhang H, Wang P, Zhang Q, Ann Am Thorac Soc. 2019 Dec 13. doi: 10.1513/AnnalsATS.201804-236OC. https://www.atsjournals.org/doi/abs/10.1513/AnnalsATS.201804-236OC