A 4-month-old female infant, born prematurely at 30 weeks and weighing 1,550 g, was hospitalized after 4 days of cough and fever. Her past history included a controlled premature birth by cesarean section due to placenta previa. She suffered from a brief period of mechanical ventilation and administration of exogenous surfactant after being born. After admitted, mild bilateral lung coarse rales were found on physical examination. Laboratory tests results showed a white blood cell count of 22.9x109 cells/L containing 58.2% neutrophils and a C-reactive protein concentration of 28 mg/L. Chest radiography exhibited patchy shadows localized to the right lung and lower left lung (Figure 1A). Subsequent computed tomography (CT) detected multiple masses and small nodules across both lungs with mediastinal lymph node involvement (Figure 1B and C). The patient was then started on intravenous ceftriaxone. Bronchoscopy revealed minimal overlying airway secretions and airway patency extending from the upper respiratory tract to the lungs; 3-9 acid-fast bacilli organisms/100 high-power fields were found in bronchoalveolar lavage fluid (BALF) and gastric aspirate by Ziehi-Neelsen staining. Thus, the patient was suspected of harboring pulmonary tuberculosis infection and treated with isoniazid, rifampin, and pyrazinamide. Although both tuberculin skin test and interferon gamma (IFN-gamma) release assays were negative, mycobacterial liquid cultures of bronchoalveolar lavage and gastric aspirate were positive at 118 and 86 hrs of culture, respectively. Isolated mycobacteria were identified (with a confidence level of 84%) as MABC using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (Vitek MS system, bioMerieux, France), supporting a diagnosis of MABC pulmonary disease. Immunologic evaluation results, including serum immunoglobulin levels and flow cytometric lymphocyte phenotyping were as follows: IgG 4.96 g/L (normal range 1.8-8 g/L), IgM 1.00 g/L (normal range 0.2-1 g/L), IgA 0.225 g/L (normal range 0.08-0.8g/L), IgE <5.00 IU/mL (normal range <=15 IU/mL), CD3+ cells 69.4% (normal range 55-82%), CD4+ cells 53.9% (normal range 55-57%), CD8+ cells 14.9% (normal range 11-25%), B cell 23.2% (normal range 11-45%), which were basically normal. However, natural killer (NK) cell level was 3%, which is below normal range 7-40%. In the review after 3 months, NK cell level raised to 10%. Whole exon sequencing (WES) was then performed and detected no pathogenic mutations, ruling out genetic disorders such as cystic fibrosis and primary immunodeficiency disease as factors contributing to exacerbation of MABC pulmonary disease in our patient. The subject family has no other case of MABC infection or immune-compromised individuals. According to expert consensus regarding diagnosis and treatment of NTM diseases, the therapy was modified to include oral clarithromycin (7.5 mg/kg, q12 h), linezolid (10 mg/kg, q8 h), and intravenous imipenem (15 mg/kg, q6 h). Due to the possibility of other mycobacterial infections, rifampicin (15 mg/kg/day) and ethambutol (15 mg/kg/day) were also administered. Subsequently, the patient's temperature returned to normal after 1 week and her cough gradually reduced, prompting cessation of intravenous imipenem administration. She was discharged after 25 days of hospitalization.
After an additional 3 months of outpatient therapy, her chest CT remained unchanged and the patient exhibited recurrence of fever with wheezing. The white blood cell count was 17.6x109 cells/L, of which 47.4% were neutrophils, with a C-reactive protein concentration of 30 mg/L. Bronchoscopy revealed an excrescent obstruction of the sub-branch of the right lower bronchi. Acid-fast staining microscopy and mycobacterial cultures of BALF and gastric aspirate were negative. The isolates that had been preserved during the first hospital stay were sent to the National Tuberculosis Clinical Laboratory of Beijing Chest Hospital for drug susceptibility testing (DST) and further strain identification. DST was carried out according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Final tested drug concentrations were as follows: clarithromycin 0.0625-32 mug/mL, amikacin 0.5-256 mug/mL, moxifloxacin 0.0625-32 mug/mL, cefoxitin 0.5-256 mug/mL, linezolid 0.25-128 mug/mL, imipenem 0.25-128 mug/mL, meropenem 0.25-128 mug/mL, and doxycycline 0.0625-32 mug/mL.
The minimum inhibitory concentration (MIC) of each drug was determined using the CLSI-recommended broth microdilution method performed in 96-well plates. DST demonstrated that isolates were susceptible to clarithromycin (MIC 0.25-0.5 mug/mL), amikacin (MIC 1-2 mug/mL), moxifloxacin (MIC 1 mug/mL), cefoxitin (MIC 4-8 mug/mL), and linezolid (MIC 1 mug/mL), with intermediate susceptibility to imipenem (MIC 8 mug/mL) and resistance to meropenem (MIC 64 mug/mL) and doxycycline (MIC >32 mug/mL). The isolates had no inducible resistance to clarithromycin, as they were susceptible to clarithromycin at both days 3 and 14.
DNA sequence analysis of the ribosomal gene internal transcribed spacer (ITS) and rpoB, and hsp65 genes was performed to identify the subspecies of causative agent. Bacterial DNA extracted using the boiling method was used as a template for PCR. PCR primer pairs were as follows: 5'-AAGTCGTAACAAGGTARCCG-3' and 5'-TCGCCAAGGCATCCACC-3' for the ribosomal gene ITS region, 5'-GGCAAGGTCACCCCGAAGGG-3' and 5'-AGCGGCTGCTGGGTGATCATC-3' for rpoB, and 5'-ATCGCCAAGGAGATCGAGCT-3' and 5'-AAGGTG-CCGCGGATCTTGTT-3' for hsp65. PCR products were purified and sequenced by TsingKe Biotech Corp. (Beijing, China). Species identification was accomplished using BLAST searching that ultimately identified patient isolates as M. abscessus subsp. massiliense (with sequence identity of 99%).
After consultation with physicians specializing in NTM disease from Beijing Chest Hospital, we treated the patient with intravenous cefoxitin (40 mg/kg q8 h), oral azithromycin (10 mg/kg/d), and moxifloxacin (10 mg/kg/d). After 3 months of treatment using this regimen, chest radiography revealed improvement, with white blood cell count (8.65x109 cells/L) and C-reactive protein concentration (<8 mg/L) both returning to normal ranges (4-10x109 cells/L and 0-8 mg/L, respectively). Cefoxitin was discontinued after 4 months of use.
Monitoring for adverse drug events was performed monthly. No obvious adverse drug reactions were observed. Blood platelet counts ranged from 152x109 cells/L to 298x109 cells/L (normal range 100-400x109 cells/L). Ranges of aspartate aminotransferase were 12-38 U/L (normal range 5-40 U/L), of alanine aminotransferase were 8-26 U/L (normal range 5-40 U/L), of serum total bile acid were 5-8 micromol/L (normal range 0-10 micromol/L), of urea were 1.8-5.2 mmol/L (normal range 1.7-7.1 mmol/L), and of creatinine were 32.1-52.2 micromol/L (normal range 30-80 micromol/L). The ECG (electrocardiogram) was normal. After 12 months of antibiotic therapy, bronchoscopy revealed no excrescent obstruction or airway patency. Chest CT showed that most lung lesions had been absorbed, with strip shadows visible in both lungs (Figure 2A and B). Moxifloxacin was discontinued; however, based upon the recommendation of NTM disease specialists, the patient continued to receive oral azithromycin and cefprozil for 4 months, with cessation of all treatment after 16 months of antibiotic therapy. Upon examination at 3 and 6 months after completion of therapy, the patient was in good clinical condition. The recent laboratory tests results showed a white blood cell count of 8.2x109 cells/L containing 49.6% neutrophils and a C-reactive protein concentration <8 mg/L. The patient will continue to receive regular follow-up by mycobacterial disease physicians.
Chest radiograph and chest HRCT scan on admission. (A) showed patchy shadows in the right lung (arrows) and the lower left lung (arrow).