# Cultures for acid-fast bacilli: are we being good stewards?

## TL;DR

This study examines the overuse of acid-fast bacilli cultures in clinical settings and suggests implementing testing criteria to reduce unnecessary testing and healthcare costs.

## Contribution

The study identifies patterns of inappropriate AFB culture use and proposes criteria to improve stewardship and reduce costs.

## Key findings

- Only 4.72% of patients had positive AFB culture results, with many likely being contaminants.
- Bone specimen cultures had a very low positivity rate (0.48%), indicating limited clinical utility.
- Medical subspecialties ordered the majority of AFB cultures, often without clear clinical justification.

## Abstract

To describe the use of cultures for acid-fast bacilli (AFB) and situations in which AFB cultures are unlikely to be of clinical benefit.

Retrospective descriptive study of AFB cultures submitted to Sentara Health microbiology laboratory from December 1, 2021, to December 1, 2023. Data were collected from the electronic medical record and included patient demographics, the service line that ordered the culture, specimen source, and culture results.

Sentara Healthcare System.

All patients who had specimens submitted to the microbiology laboratory during the study period were included.

A total of 13,944 AFB cultures from 8,243 patients were collected during the study period. Of these, 4.72% (n = 389) patients had a positive result, and 40 of 680 positive cultures were likely contaminants or non-mycobacterial. The average number of days between culture collection and positive results was 84.32 days (SD = 49.64) and 56.25 days (SD = 8.32) for negative results. Most cultures were ordered by medical subspecialties (44.06%, n = 6,144), followed by orthopedic providers (23.34%, n = 3,254) and surgical subspecialty providers (16.11%, n = 2,246). Most specimens were pulmonary (n = 6,620) with 619 (9.35%) positive cultures. Of 3,561 AFB cultures ordered from bone specimens, only 17 were positive (0.48%). The number of specimens processed by the microbiology laboratory required 2 full-time microbiology technicians to process specimens.

Many AFB cultures were sent from patients who did not have clinical scenarios consistent with mycobacterial disease and cultures were not clinically indicated. Implementation of testing criteria could decrease AFB cultures and healthcare costs.