# Diagnostic Usefulness of Liquid Culture Medium for Mycobacterium avium-intracellulare Complex Lung Disease: A Single-Centre, Retrospective Study

## TL;DR

This study shows that using liquid culture improves the early diagnosis of Mycobacterium avium-intracellulare complex lung disease compared to traditional solid culture methods.

## Contribution

The study demonstrates the diagnostic superiority of liquid culture over Ogawa culture for MAC-LD in a large retrospective cohort.

## Key findings

- Liquid culture had a 98.3% positivity rate compared to 44.9% for Ogawa culture.
- 75.5% of patients would have experienced delayed diagnosis without liquid culture.
- 25.3% of smear-positive specimens were positive only on liquid culture.

## Abstract

Background

The diagnosis of Mycobacterium avium-intracellulare complex lung disease (MAC-LD) requires two or more positive sputum cultures. Few reports have examined the usefulness of adding liquid culture to conventional solid culture for diagnosing MAC-LD.

Methods

A retrospective, cohort study of patients examined at Kurashiki Central Hospital in Japan with a confirmed diagnosis of MAC-LD between January 1, 2002, and June 20, 2021, was conducted. The primary endpoint was the culture positivity rate, which was compared between the liquid and Ogawa culture media in patients who underwent sputum culture using both methods. Secondary endpoints were the culture positivity rate in smear-positive specimens and the positivity rate by radiological type.

Results

The study, which involved 351 patients and 702 specimens, showed a higher positivity rate for liquid culture (n=690, 98.3%) than Ogawa culture (n=315, 44.9%). Overall, 265 patients (75.5%) would have had delayed MAC-LD diagnosis without liquid medium being used. Of the 95 smear-positive specimens, 71 (74.7%) were positive on both cultures, whereas 24 (25.3%) were positive only on liquid culture. The positivity rate of Ogawa culture varied by radiological type.

Conclusions

Liquid culture is more valuable for the early diagnosis of MAC-LD than Ogawa culture.