A Ten-Year Study of the Epidemiology and Antimicrobial Resistance of Bacterial Pathogens Associated with Otitis in Crete, Greece.

BACKGROUND

Otitis is a very common infection, mainly affecting children, and the main indication for prescribing antibiotics. This study investigated the epidemiology and antibiotic resistance profile of bacterial pathogens asso-ciated with otitis in patients of all ages in Crete, Greece.

METHODS

From January 2013 through December 2022, patients diagnosed with otitis, based on clinical signs and symptoms and otoscopy findings, were enrolled in the study. Ear discharge samples were collected by tympanοcentesis or by using sterile swabs and were promptly transported to the microbiology laboratory for further processing. Cultures for bacterial pathogens were performed according to laboratory protocols. Bacteria were identi-fied by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry and antimicro-bial susceptibility testing by Vitek 2 system.

RESULTS

Out of the 939 samples examined, 600 (63.9%) were positive for bacterial pathogens. P. aeruginosa was the most prevalent microorganism detected (29.5%), followed by S. aureus (18.9%) and Enterobacterales (12.8%). The isolation rate of P. aeruginosa significantly increased during the study period (p = 0.0001). P. aeruginosa resistance rates to ticarcillin/clavulanate, piperacillin/tazobactam, ceftazidime, cefepime, aztreonam, imipenem and meropenem were 6.4%, 3.4%, 3.4%, 3.8%, 3.3%, 2.1%, and 2.1%, respectively. Ceftazidime resistance remained around the same levels during the study period, while resistance to piperacillin/ tazobactam, cefepime, imipenem, and meropenem doubled over the years 2018 - 2022 (p = 0.48, p = 0.49, p = 0.65, and p = 0.65, respectively). S. aureus penicillin-resistance was extremely high (87.4%). Resistance rates to methicillin, erythromycin, and clindamycin were 21.2%, 14.6%, and 11.9%, respectively. Forty-one percent of the methicillin-resistant strains were multidrug-resistant (MDR). All isolates were susceptible to gentamicin, rifampicin, linezolid, daptomycin, tigecycline, teicoplanin, and vancomycin. Among Enterobacterales, high rates of resistance were observed for ampicillin, amoxicillin/ clavulanate, colistin, tigecycline, and tetracycline, ranging from 34.1% to 82.5%.

CONCLUSIONS

P. aeruginosa, S. aureus, and the Enterobacterales are the predominant bacterial pathogens causing otitis in our area. Regarding Gram-negatives, although resistance rates to commonly-used antibiotics are low, they are increasing over time. Continued surveillance of the prevalence and antimicrobial susceptibility of bacterial pathogens causing otitis is necessary to reassess updated antimicrobial policies and develop appropriate guidelines.