# Legionella maceachernii Pneumonia Presenting as a Cavitary Lesion in an Immunocompromised Patient

## TL;DR

An immunocompromised patient developed pneumonia caused by the rare Legionella maceachernii, diagnosed using DNA sequencing due to the limitations of traditional tests.

## Contribution

This case highlights the use of cell-free DNA sequencing for identifying rare Legionella species in immunocompromised patients.

## Key findings

- Legionella maceachernii was identified as the cause of pneumonia in an immunocompromised patient.
- Cavitary lesions were observed as a radiological finding in this case.
- Molecular testing via cell-free DNA sequencing provided a timely and accurate diagnosis.

## Abstract

Legionella is an intracellular, gram-negative bacterium known as a less common cause of pneumonia, which has become a public health concern in recent years due to increased incidence. Legionella pneumophila is recognized as the most common cause of Legionnaires' disease. Other Legionella species, including Legionella maceachernii, have been rarely described as causes of Legionnaires' disease. Moreover, cavitary lesions as radiological findings in patients with Legionnaires' disease are uncommon but have been reported, especially in immunocompromised patients. Although the gold standard for diagnosis is a positive culture, the need for special media and extended time for growth can overlook or delay diagnosis. Additionally, urine antigen testing will miss detection of species other than Legionella pneumophila serogroup 1. Molecular testing, although not routinely performed, is a promising tool for early detection and identification of other Legionella species. We present a case of an immunocompromised patient presenting with fevers and a cavitary lesion, diagnosed with Legionella maceachernii through cell-free DNA sequencing.