To investigate the application value of metagenomic next-generation sequencing (mNGS) technology for the diagnosis and treatment of patients with Acinetobacter baumannii (Ab) pneumonia mixed infection in intensive care units (ICU).

The basic data, bacterial culture, mNGS test results and antimicrobial drug application of 84 patients who underwent both alveolar lavage fluid mNGS technique and traditional pathogen detection for pneumonia at the Affiliated Hospital of Yangzhou University from January 2019 to May 2021 were collected, retrospectively. All patients were divided into colonized bacteria group (25 cases), single infection group (29 cases) and mixed infection group (30 cases) according to the diagnostic criteria of Ab infection and mNGS test results. Data such as inflammatory indicators , the Simpson’s diversity index (SDI), time and intensity of antimicrobial drugs, and total drug costs were normally distributed and were analyzed by t-test or ANOVA test, and distribution of age, underlying disease, fever, different clinical efficacy and proportion of treatment conversion were count data and were analyzed by χ² tests.

Total of 84 patients were positive for traditional pathogen testing and mNGS testing, including 25 cases with Ab colonization and 59 cases with Ab pneumonia; 44 males and 40 females, aging [65.4 (62, 68)] years old. During the mNGS test, 30 cases [50.85% (30/59)] were with mixed infections; but only 3 cases [5.08% (3/59)] had mixed infections according to the traditional test, which was significantly lower than that of mNGS test (χ² = 30.667, P < 0.001). The top three pathogens with mixed infections detected by mNGS were human herpes virus (7 cases), Streptococcus pneumoniae (5 cases) and Pneumocystis jiroveci (5 cases). The SDI were (0.77 ± 0.11), (0.38 ± 0.16) and (0.34 ± 0.17) in colonized bacteria group, single infection group and mixed infection group, respectively, with significant difference (F = 65.411, P < 0.001). Compared with single infection group, white blood cell count [(11.56 ± 1.34) × 10⁹/L vs. (10.61 ± 1.91) × 10⁹/L: t = 2.211, P = 0.031], rate of neutrophil ratio [(77.13 ± 3.90) % vs. (75.09 ± 3.67) %: t = 2.068, P = 0.043], C-reactive protein [(14.32 ± 4.01) mg/L vs. (12.49 ± 2.78) mg/L: t = 2.024, P = 0.048], cost of antimicrobial drugs (5 982.67 ± 740.38) yuan vs. [(5 505.00 ± 866.74) yuan: t = 2.279, P = 0.026], intensity of of antimicrobial drugs use (136.33 ± 9.62) 100 people/day vs. [ (130.69 ± 10.43) 100 people/day: t = 2.161, P = 0.035) ], hospitalization duration [(14.00 ± 4.45) days vs. (11.45 ± 2.73) days: t = 2.664, P = 0.010], total drug costs [(14 437.73 ± 2 377.51) yuan vs. (12 704.24 ± 3 138.12) yuan: t = 2.397, P = 0.020], and the period for body temperature returning to normal [(3.83 ± 1.72) days vs. (4.97 ± 2.24) days: t =-2.178, P = 0.034] of patients in mixed infection group were significantly different. The efficiency of patients in single infection group was significantly higher than that of mixed infection group (82.76% vs. 56.67%; χ² = 4.735, P = 0.047).

Alveolar lavage fluid mNGS technique has obvious advantages in detecting mixed infection of Ab pneumonia, which could assist clinical antimicrobial selection and promote patients’ rehabilitation.