A 41-year-old woman with a history of cough variant asthma and chronic sinusitis visited her primary care physician in October 2020 with a complaint of bloody sputum. Upon consultation, she was not provided with any immunosuppressive medications, including inhaled corticosteroids. The patient repeatedly underwent nasal irrigation and gargling. Despite treatment with clarithromycin, amoxicillin, and amoxicillin/clavulanic acid, she continued to experience symptoms and increased purulent sputum production. In December 2020, the patient underwent further examinations at a general hospital. Chest computed tomography (CT) did not show any obvious abnormalities, while three sputum culture tests consistently detected the presence of M. abscessus.
She was referred to our department in April 2021 and tested positive for M. abscessus subsp. abscessus on sputum culture. She had worsening symptoms of possible posterior rhinorrhoea (phlegm dripping into the throat) and showed mild sinusitis on sinus CT; hence, M. abscessus infection of the sinuses was suspected. Nasal endoscopy did not show any abnormalities in the nasal cavity, such as purulent nasal discharge. Polymerase chain reaction (PCR) tests for Mycobacterium tuberculosis/NTM and acid-fast bacilli (AFB) cultures of the nasal secretions yielded negative results.
Positron emission tomography/computed tomography (PET/CT), performed in June 2021 to identify the focus of infection, showed 18-fluorodeoxyglucose accumulation with a maximum standardized uptake value of 3.5 in the right nasopharyngeal wall (Figure 1a). Laryngeal endoscopy revealed purulent discharge in the right nasopharynx (Figure 1b). Initially, the purulent nasopharyngeal discharge showed positive results on smear test but negative for AFB on culture test. Repeat culture tests of purulent discharge collected by laryngeal endoscopy were performed; the purulent discharge collected in December 2021 tested positive for M. abscessus subsp. abscessus leading to a diagnosis of M. abscessus disease of the nasopharynx. Drug susceptibility tests indicated that the isolate was susceptible to amikacin and resistant to macrolides (Table 1). Specimens collected from the patient's kitchen and bathroom tested negative for AFB. 
The patient was hospitalized and treated with amikacin, imipenem/cilastatin, azithromycin, and clofazimine for 28 days. After discharge, the patient was treated with amikacin, azithromycin, clofazimine, and sitafloxacin, a new fluoroquinolone, for four months. Since sitafloxacin's minimum inhibitory concentration for M. abscessus is reported to be low, it is used in clinical settings in Japan. The posterior rhinorrhoea improved, and laryngeal endoscopy performed in February 2022 revealed the absence of purulent discharge in the nasopharynx (Figure 1c). In addition, both sputum smear and culture tests yielded negative results at the end of the patient's treatment. PET/CT performed in May 2022 confirmed the disappearance of the previously observed abnormal accumulation in the right nasopharyngeal wall (Figure 1d). The patient was followed up in an outpatient clinic and revealed no evidence of recurrence. Whole-genome sequencing of M. abscessus subsp. abscessus constitutively isolated from the patient revealed that all strains belonged to a phylogenetic cluster, ABS-GL4 (Figure 2a). The pairwise SNP distance between these isolates was less than 10 SNPs (Figure 2b). Mutations in the 23S rRNA (rrl) gene conferring macrolide resistance were not detected in these isolates, but they carried the functional erm(41) gene (Figure 2a), which was expected to induce macrolide resistance. In addition, the strains did not harbour the known A1375G substitution in the 16S rRNA (rrs) gene, which confers amikacin resistance (Figure 2a).