OBJECTIVE: To determine abstracts' adherence to the Consolidated Standards of Reporting Trials for Abstracts (CONSORT-A) statement and to explore the factors associated with reporting quality. DESIGN: An observational study. SETTING: Abstracts of randomised controlled trials published between 2010 and 2019, found searching the MEDLINE database. PARTICIPANTS: A total of 451 abstracts of the clinical trials infections were included. PRIMARY AND SECONDARY OUTCOME MEASURES: Abstracts' reporting quality was determined by assessing their adherence to 17-item CONSORT-A checklist, with overall score being calculated as the sum of items that were adequately reported for each abstract. Additional factors that might influence the reporting quality of the abstracts were analysed, with univariate and multivariate linear regression used to determine how those factors influenced the overall reporting quality. RESULTS: Included abstracts had an overall median quality score of 8/17 (IQR 7-9). Large proportions of abstracts adequately reported interventions, participants, objectives, numbers randomised and conclusions (97.1, 99.3, 89.1. 94.7 and 98.4% of abstracts, respectively). Trial design, randomisation, blinding and funding were severely under-reported with only 8.0, 2.7, 11.0 and 2.0% of abstracts reporting each item. Overall quality scores for abstracts were higher in association with CONSORT-A endorsement (B=5.698; 95% CI 1.781 to 9.615), pharmacological interventions (B=4.063; 95% CI 0.224 to 7.902), multicentre settings (B=5.057; 95% CI 2.370 to 7.743), higher numbers of participants (B=3.607; 95% CI 1.272 to 5.942), hospital settings (B=4.827; 95% CI 1.753 to 7.901) and longer abstracts (B=3.878; 95% CI 0.787 to 6.969 for abstracts with 251-300 words and B=7.404; 95% CI 3.930 to 10.878 for abstracts with more than 300 words). CONCLUSIONS: The overall reporting quality of abstracts was inadequate. The endorsement of CONSORT-A guidelines by more journals might improve the standards of reporting.