Epidemiological and clinical characteristics of ammonia-producing microorganisms in the lungs of patients with severe pneumonia: a multicentre cohort study

Background: Ureaplasma urealyticum, Ureaplasma parvum, and Mycoplasma hominis were widely known as ammonia-producing microorganisms and can cause hyperammonemia, leading to cerebral edema and altered consciousness, which represent serious complications in lung transplant recipients. However, there is limited knowledge on the epidemiology and outcomes of infections caused by U. urealyticum, U. parvum, and M. hominis in non-transplant patients with severe pneumonia in the ICU.

Methods: Patients with severe pneumonia who underwent clinical metagenomics of bronchoalveolar lavage fluid (BALF) at the intensive care units (ICUs) of 17 medical centers from January 2019 to March 2023 were enrolled. All cases were divided into the positive group and the negative group based on whether U. urealyticum, U. parvum, or M. hominis was detected in lower respiratory tract. The clinical characteristics and outcomes were compared among the groups. The survival analysis after propensity score matching (PSM) was used to evaluate whether the mortality rate of U. urealyticum, U. parvum, and M. hominis positive patients were increased. Multivariate logistic regression was used to evaluate whether these microbials positivity were a risk factor for central nervous system dysfunction.

Results: In a total number of 1737 patients, 55 patients (3.17%) in the positive group and 1682 patients (96.83%) in the negative group. Patients in the positive group were younger, had a greater proportion of male patients, and had a longer time from ICU admission to clinical metagenomics testing. In contrast, the negative group had a higher proportion of patients with cerebrovascular disease. After PSM, there was no statistically significant difference in 28-day mortality following ICU admission between the two groups (hazard ratio [HR], 0.842; 95% confidence interval [CI], 0.489-1.451; p = 0.536). Multivariate logistic regression analysis showed an association between the detection of U. urealyticum, U. parvum, or M. hominis and neurological dysfunction (odds ratio [OR], 1.84; 95% CI 1.04-3.24; p = 0.035).

Conclusion: The detection of U. urealyticum, U. parvum, or M. hominis in the lungs of patients is associated with neurological dysfunction.