M. abscessus Cluster in Southeast Florida Likely Due to Rainfall, Soil

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by Vanda Pinto, PhD |

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A cluster of Mycobacterium abscessus (M. abscessus), a difficult-to-treat bacteria that causes lung damage, particularly in people with cystic fibrosis (CF), was identified in the southeastern Florida, a recent study reported.

According to its findings, patients who tested positive for a nontuberculous mycobacteria (NTM) infection, including M. abscessus, were more likely to be living in areas with a higher average annual rainfall and increased levels of sodium in the soil.

The research, “Environmental predictors of pulmonary nontuberculous mycobacteria (NTM) sputum positivity among persons with cystic fibrosis in the state of Florida,” was published in the journal PLOS ONE.

NTM infections can cause NTM lung disease, which damages the lung tissue and is resistant to treatment. Among the several types of NTM, M. abscessus and Mycobacterium avium (M. avium Complex or MAC) are the most commonly found in CF patients.

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Since nontuberculous mycobacteria are naturally found in soil, water, and dust, several studies previously attempted to analyze the relationship between environmental factors, such as soil properties, and NTM infections.

Researchers have pinpointed several regions in the United States where NTM infections are most common. Florida, with the highest prevalence of such infections, is at the top of this list. In this state, the five-year NTM prevalence, defined as the number of people who had an NTM infection within the previous five years, was 31% from 2010 through 2014.

Florida’s high rate of NTM infections prompted a team of researchers at the National Institutes of Health, and a scientist at the Colorado School of Public Health, to search for environmental predictors of NTM and to identify clusters of such infections in this state.

“Because the prevalence of PNTM [pulmonary NTM] in Florida is so high, understanding whether there are environmental predictors or geospatial clustering of NTM is of interest to the CF community and public health,” the investigators wrote.

Data spanning 2010 to 2017 from the Cystic Fibrosis Foundation Patient Registry were analyzed. The study population included patients ages 12 and older who lived in Florida for at least two consecutive years. Incident cases were those in which the patient had a positive sputum culture after one or more negative cultures. (A sputum culture detects infection-causing bacteria in the lungs or airways.)

Environmental variables — including vapor pressure, rainfall, temperature, and the levels of minerals (copper, sodium, manganese, calcium and molybdenum) in the soil and water — were examined, selected based on previous reports that identified them as predictive of NTM infection.

A total of 979 patients were included in the study, of which 261 (26.7%) were classified as positive for NTM. In this group, 109 patients (41.8%) had a MAC infection and 118 (45.2%) had M. abscessus.

A high-risk cluster associated with M. abscessus was identified in Southeast Florida, an area that comprises Broward, Miami-Dade, and Palm Beach counties.

Additionally, statistical analysis revealed that patients with a positive sputum culture were most likely to be residing in areas, determined by ZIP code, with higher rainfall. In fact, the likelihood of a positive culture increased by 34% for each point increase in average annual precipitation.

Soil geochemistry also correlated with NTM positivity, with NTM infection 92% more likely with each point increase in the soil’s sodium concentration. In contrast, a 40.7%  lower risk of NTM infection was associated with a point increase in soil levels of manganese.

More detailed studies are needed, the scientists noted,  since environmental factors that impact NTM prevalence can differ from one region to the next.

“Because persons with CF are at increased risk for NTM infection, continued studies to determine high-risk geographical areas and specific predictors of disease are critical so that precautions can be taken to reduce risk of exposure,” they concluded.