Drying Does Not Clear Nebulizers of NTM Bacteria, Study Finds

Nontuberculous mycobacteria (NTM), a type of infectious bacteria, is able to survive being dried for a full day, a study found, suggesting that drying is not a sufficient way to disinfect nebulizers used by people with cystic fibrosis (CF).

The study, “Susceptibility of the Mycobacterium abscessus complex to drying: Implications for nebulizer hygiene in patients with cystic fibrosis,” was published in the International Journal of Mycobacteriology.

NTM refers to mycobacteria — a bacterial genus — other than Mycobacterium tuberculosis (which causes tuberculosis) and Mycobacterium leprae (which causes leprosy). NTM are increasingly being recognized as a common and worrisome infectious agent in people with CF.

Patients use inhaled therapies delivered via a nebulizer. Cleaning nebulizers of residual bacteria after their use is important for minimizing the risk of infection in these people.

It is commonly recommended for nebulizers to be washed and then dried between each use. Previous research has demonstrated that drying can kill Pseudomonas aeruginosa, another type of infectious bacteria that is of concern in CF. However, whether drying can also kill NTM is unclear.

Researchers in Northern Ireland assessed whether drying,”emulating that of the CF patient and their practices in daily nebulizer care and hygiene,” could kill three different types of NTM. The NTM bacteria they studied were Mycobacterium abscessus, subspecies massiliense; M. abscessus, subspecies bolletii; and M. abscessus, subspecies abscessus.

For each type, two clinical isolates were tested.

Bacteria were placed on plastic surfaces mimicking a nebulizer, and dried for a day. Both drying at room temperature and drying in an incubator (at 37 C, about 99 F) were tested.

Their experiments recreated “the typical manipulations of the nebulizer during nebulizer cleaning,” the researchers wrote.

After drying, the team tested whether bacteria were able to grow in a culture in the lab — that is, whether or not they were alive.

In all experiments, no evidence suggested that drying killed these bacteria. All NTM isolates tested were viable after drying for 24 hours, regardless of the M. abscessus species tested or the drying method used.

“This study indicates that drying, either passively or actively, for 24 h at room temperature, is unable to eradicate all M. abscessus organisms from dry plastic surfaces,” the researchers concluded.

“Within the context of nebulizer hygiene, this means that these NTM organisms would be able to survive on a washed nebulizer following drying for 24 h, which has not undergone any formal disinfection protocol, which can eradicate NTM organisms,” they added.

Based on the results, the team suggested that CF patients “seek an effective alternative control to drying for NTM eradication,” such as steam or heat disinfection.