Hospitalized patients in France carry Gram-negative bacilli in their oropharynx far more often than healthy people, according to a prospective multicenter case-control study published in Antimicrobial Resistance & Infection Control. The finding matters because oropharyngeal colonization with these organisms is considered a major factor in the development of ventilator-associated pneumonia, the most common severe nosocomial infection in intensive care units, which drives significant inpatient morbidity and mortality as well as antibiotic consumption.
The study screened 100 healthy subjects and 389 hospitalized patients admitted either to an ICU or to three different surgery wards: orthopaedic, digestive or thoracic. Samples from hospitalized patients were collected at admission, on day 5 and on day 10 or at discharge, while healthy subjects were sampled only on the day of inclusion. Isolates were identified, tested for antibiotic susceptibility, and Enterobacterales strains resistant to third-generation cephalosporins were sequenced. Demographic data and clinical characteristics were collected and risk factors analysed.
Oropharyngeal colonization by Gram-negative bacilli was significantly higher in hospitalized patients on admission than in healthy subjects, with an odds ratio of 9.0 (95% confidence interval 3.2 to 25.1; P < 0.0001). The authors report that the prevalence of this colonization is very low in healthy subjects, making the contrast with admitted patients particularly striking.
The risk of colonization varied significantly by ward type. Using orthopaedic surgery as the reference category, which showed the lowest risk, the risk difference for the other wards ranged between 21.4 and 25.2 (P = 0.0004). In other words, patients admitted to orthopaedic surgery wards were significantly less likely to be colonized than those admitted to the other wards studied.
Beyond ward type, several factors were significantly associated with colonization at admission: male gender, tobacco use and chronic alcohol consumption, as well as several comorbidities including solid-organ cancers and cardiovascular disease. This pattern suggests that colonization is correlated with intrinsic characteristics of the patients rather than being uniform across all hospital admissions.
Acquisition of new colonization during hospitalization was low for all patients, indicating that much of the burden detected at admission was already present when patients entered the hospital. This observation reinforces the study’s conclusion that patient characteristics, rather than events occurring during the hospital stay, are the dominant correlates of colonization at admission.
Among hospitalized patients, 3.5% of oropharyngeal swabs were positive for third-generation cephalosporin-resistant Enterobacterales. Sequencing revealed high-risk transmissible clones among these isolates, including ST405 Klebsiella pneumoniae and O25:H4 ST131 fimH30 Escherichia coli resistant isolates. The authors report that asymptomatic oropharyngeal carriage of such high-risk transmissible clones was observed in patients admitted to the ICU.
The study was prospectively registered on ClinicalTrials.gov (NCT02839980) on 21 July 2016. The authors conclude that asymptomatic carriage of high-risk clones should be considered in order to prevent inadequate treatment and delays in appropriate management of hospital-acquired pneumonia. Because the study was conducted in French hospitals and reported as an accepted manuscript shared early for faster access, with a final version of record to follow, the findings should be read in that context; the work establishes associations between patient characteristics and colonization status rather than demonstrating the effect of any intervention.
Subject of Research: Oropharyngeal colonization by Gram-negative bacilli in hospitalized patients compared with healthy subjects
Article Title: Oropharyngeal colonization by Gram-Negative bacilli is higher in hospitalized patients than in healthy subjects: a French case – control study
Article References: Landraud, L., Messika, J., Martinez, C., Hajage, D., Gernez, C., Billard-Pomares, T., Duval, X., Jacquier, H., Mentec, H., Portela, A. M., Denamur, E., Ricard, J. D., the OroColi Group, Msika, S., Calabrese, D., Claudinon-Courpon, A., Martinod, E., Carbonnelle, E., Nizard, S. R., … Bercot, B. (2026). Oropharyngeal colonization by Gram-Negative bacilli is higher in hospitalized patients than in healthy subjects: a French case – control study. Antimicrobial Resistance & Infection Control. https://doi.org/10.1186/s13756-026-01831-7
Image Credits: AI Generated
DOI: 10.1186/s13756-026-01831-7
Keywords: Gram-negative bacilli, oropharyngeal colonization, ventilator-associated pneumonia, hospital-acquired pneumonia, multidrug-resistant bacteria, Enterobacterales, Klebsiella pneumoniae, Escherichia coli, intensive care unit, case-control study, antimicrobial resistance, France
News Source: Kristina Jarvis. (October 28, 2026). Hospital patients carry more throat Gram-negative bacilli than healthy people, French study finds. Scienmag.
