Characteristics of included guidelines.

Introduction
Expert opinion is widely used in clinical guidelines. No research has ever been conducted investigating the use of expert opinion in international infectious disease guidelines. This study aimed to create an analytical map by describing the prevalence and utilization of expert opinion in infectious disease guidelines and analyzing the methodological aspects of these guidelines.
Methods
In this meta-epidemiological study, systematic searches in PubMed and Trip Medical Database were performed to identify clinical guidelines on infectious diseases, published between January 2018 and May 2023 in English, by international organizations. Data extracted included guideline characteristics, expert opinion utilization, and methodological details. Prevalence and rationale of expert opinion use were analyzed descriptively. Methodological differences between groups were analyzed with Chi-square and Mann-Whitney U Test.
Results
The analysis covered 66 guidelines with 2296 recommendations, published/endorsed by 136 organizations. Most guidelines (79%) used systematic literature searches, 42% provided search strategies, and 38% presented screening flow diagrams and conducted risk of bias assessments. 48.5% of the guidelines allowed expert opinion, most of which included expert opinion as part of the evidence hierarchy within the grading system. Guidelines allowing expert opinion, compared to those which do not, issued more recommendations per guideline (48.82 vs.19.13, p<0.001), and reported fewer screening flow diagrams (25% vs. 65%, p = 0.002), and less risk of bias assessments (19% vs.78%, p<0.001).
Conclusions
Expert opinion is utilized in half of assessed guidelines, often integrated into the evidence hierarchy within the grading system. Its utilization varies considerably in methodology, form, and terminology between guidelines. These findings highlight a pressing need for additional research and guidance, to improve and advance the standardization of infectious disease guidelines.