Strains of mycobacteria that do not cause tuberculosis but do cause lung infections
are becoming more virulent and spreading fast according to a new study. Non-tuberculous mycobacteria
are rampant in the natural environment and are inhaled by most people. Among these, the Mycobacterium avium complex is the most commonly found, but there are over 160 different species of them and not much research have been done on them.
causes sickness in a very 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. Also 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 typical 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.
For treatment, 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 researchers in the new study 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.
The researchers 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.
Also, 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.
“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.” commented Dr Kevin Winthrop during a phone interview with
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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.
Physicians 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.
However, the researchers did warn that rising exponential rates could indicate that the bacterial strains could be mutating and becoming more virulent.
The medical 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 non-availability of exact codes; and the possible lack of national representation as the number of participants in this health plan varied significantly across the country.
Reference: 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