Legionella micdadei: A Forgotten Etiology of Growing Cavitary Nodules: A Case Report and Literature Review

Abstract

Background. Legionella micdadei is a Gram negative bacterium that can stain weakly acid fast. It was first described in 1979 after immunosuppressed patients developed pneumonia at a Pittsburgh VA, initially given the name Pittsburgh Pneumonia Agent. It is the second most common Legionella species causing infection after pneumophila, and typically infects immunocompromised hosts. It is not easy to be cultured which makes diagnosing difficult. Case Presentation. A 31-year-old female with ulcerative colitis, primary sclerosing cholangitis, and cirrhosis presented with fever, chills, shortness of breath, dry cough, and chest pain for five days after being started on immunosuppression for autoimmune hepatitis two months earlier. The first chest CT showed small bilateral cavitary nodules. The nodules continued to grow on subsequent imaging despite what was thought to be appropriate therapy. A transthoracic biopsy was performed which grew Legionella micdadei and the patient improved after being treated with levofloxacin. Conclusion. Legionella micdadei is an atypical pathogen known to cause pneumonia in immunosuppressed patients. This case highlights a typical presentation of an atypical infection not commonly thought about and should be considered when nodules are growing despite being on broad antimicrobial therapy.

Pneumonia and pulmonary abscess due to Legionella micdadei in an immunocompromised patient

“…L. micdadei are ubiquitous bacteria responsible for pneumonias that preferentially affect profoundly immunosuppressed people, as was our patient under immunosuppressive medications and more recently added high-dose corticosteroids. 1,2,[4][5][6][7] The reasons why L. micdadei are rarely found in healthy people are not clear. Even if L. micdadei and L. pneumophila share virulence genes, it seems that L. micdadei are less virulent than L. pneumophila, and show fewer cytotoxic capacities when cultured with macrophages.…”

“…However it is worth noting that several previously reported cases of L. micdadei infections in immunocompromised individuals have become complicated by lung abscess. 1,[5][6][7] Even though L. micdadei are responsible only for a low percentage of legionellosis cases, we believe it is important for clinicians to be aware of L. micdadei's propensity to induce pulmonary nodules that can cavitate in this high-risk population.…”

“…3 Rare cases of endocarditis, brain abscess, cellulitis, or prosthetic joint infections due to L. micdadei have been published, but it has a predilection for causing pneumonia in immunocompromised hosts. 1,2,[4][5][6][7] The mortality rate of L. micdadei infections may be around 20% in some series. 2 We report a case of L. micdadei pneumonia and discuss the difficulties encountered in establishing the diagnosis.…”

Legionnaires' disease in transplant recipients: A 15‐year retrospective study in a tertiary referral center

“…No pathognomonic clinical or imaging findings differentiated L. pneumophila from LNLP infections or other causes of opportunistic pulmonary infections. LD may present with a range of radiologic findings including nodular changes on computed tomography (Table ) that could be mistaken for fungal infection among transplant patients . Unusual presentations can also occur in this profoundly immunocompromised population.…”

Cavitary Pulmonary Nodules in an Immunocompromised Patient With Urothelial Carcinoma of the Bladder

“…Furthermore, Legionella species are gram-negative bacilli that stain poorly using Gram stain, especially if safranin is used as the counterstain, and they are difficult to observe in Gram stains of clinical specimens [ 5 ]. Therefore, Gram staining of respiratory specimens revealing polymorphonuclear leukocytes in the absence of organisms may suggest infection with Legionella species [ 7 , 8 ].…”