Pulmonary Nocardiosis: Review of Cases and an Update

Nocardia, a branching, filamentous bacteria, is widely distributed in the environment and can cause human infection in immune-compromised hosts. Inhalation of Nocardia leads to pulmonary disease. Microbiology laboratory processed the clinical samples from patients with respiratory infections. Smears were prepared from the samples and were stained and cultured. Five cases were positive for Nocardia. They were treated with the trimethoprim-sulfamethoxazole combination. The disease was cured in three patients, and two died due to other comorbid conditions leading to complications. Nocardiosis is encountered in parts of the world even where it is not endemic due to increased world travel. So physicians and laboratory staff should be aware of this and try to diagnose it. Early detection can lead to the prompt initiation of treatment and reduced mortality in these patients. Patients with disseminated or severe nocardiosis should be treated with combination therapy with two or more active agents.


Case Presentation
In the present study, five cases of pulmonary nocardiosis (PN), four males and one female, were encountered among patients attending Vallabhbhai Patel Chest Institute, a tertiary care respiratory diseases hospital in Delhi, India. They were admitted with complaints of breathlessness and increased cough with sputum production from a week to 3-month duration. They all had fever and weight loss. All were immunocompromised with four of them having the chronic obstructive pulmonary disease (COPD) with tuberculosis and one with COPD and diabetes mellitus. Sputum samples from four and bronchial alveolar lavage, bronchial aspirate, and sputum from one case showed Gram-positive filamentous branching rods with beaded appearance on Gram's staining and acid fast branching filamentous rods with beaded appearance on modified Ziehl-Neelsen staining suggestive of Nocardia. It was isolated on sheep blood agar from four cases. Patients were treated with trimethoprim-sulfamethoxazole (TMP-SMX) along with other antibiotics like amikacin and imipenem/meropenem. Three were discharged and advised to continue TMP-SMX for six months. Two of these were followed up and were completely free of symptoms, and their sputum was negative on smear and culture. Two of the patients died. Table 1 shows the details of the cases.

Discussion and Update
2.1. Introduction. Nocardia is widely distributed in dust, soil, water, and vegetable matter. Inhalation of the dust particles leads to pulmonary involvement commonly caused by N. asteroides complex. Direct inoculation of the organism can lead to infections of the skin and subcutaneous tissue. They can disseminate from pulmonary or cutaneous focus to virtually any organ.

Epidemiology and Risk Factors. Nocard first described
Nocardia in 1888 [1] which was later described by Eppinger (1890), in a man with a pulmonary disease with "pseudotuberculosis" of lungs and pleura, caseous peribronchial lymph nodes, meningitis, and multiple abscesses in the brain [2]. Nocardia consists of more than 22 species of which N. asteroides complex, comprising of N. asteroides sensu stricto, N. farcinica, N. nova, and N. abscessus, is the most common. Agricultural occupation is a risk factor for pulmonary nocardiosis. Systemic immunosuppression, corticosteroid therapy, lymphoma, sarcoidosis, systemic lupus erythematosus, chronic alcoholism, diabetes mellitus, and human immunodeficiency virus (HIV) infection are other predisposing factors. Lately, it has been observed that COPD is also a risk factor for Nocardia infection [3].   Gram's stain smear shows Gram-positive, beaded, fine, right-angled branching filaments (<1 m diameter) which may fragment to form rods and coccoid forms of varying sizes. Most isolates of Nocardia are acid fast by modified Kinyoun technique that differentiates it from Actinomyces which is not acid fast. Silver methenamine stain is equally useful and reliable as modified Ziehl-Neelsen staining [4].
Nocardia spp. grow on media used for culture of bacteria, fungi, and Mycobacteria. Typical colonies appear after three to five days. Nocardia spp. appear as either buff or pigmented waxy cerebriform colonies or have a dry, chalkywhite appearance with the production of aerial hyphae.
Some commercial identification systems like API 20C (Biomerieux) allow for rapid identification of Nocardia spp. but have the limitation of the traditional phenotypic method [5].
Molecular identification of Nocardia is not only quick and accurate but also helps in the recognition of new species. Various methods like ribotyping, polymerase chain reaction, restriction fragment length polymorphism analysis, and DNA sequencing are available [6].
DNA sequencing is currently the best tool for species identification of Nocardia. Sequencing of first 500-606 base pairs of the 5 end of 16S rRNA gene is the recommended method [6]. All these methods have their limitations and should be used with caution.
Currently, there are no serological tests available for diagnosis of active nocardiosis due to the cross-reactivity among different Nocardia species, Mycobacterium tuberculosis, Mycobacterium leprae, and other Actinomycetes [7].

Management.
Trimethoprim-sulfamethoxazole (TMP-SMX) is the mainstay of treatment and has improved the outcomes. In adults, with normal renal function and localized disease, the recommended daily dose of TMP-SMX is 5 to 10 mg/kg TMP and 25 to 50 mg/kg SMX in two to four divided doses, depending on the extent of disease. Higher initial doses (15 mg/kg TMP and 75 mg/kg SMX), given intravenously or orally, are frequently used in patients with cerebral abscesses; severe, extensive, or disseminated infection; or AIDS. Sulfonamides are the treatment of choice for disease due to N. brasiliensis. However, mortality with monotherapy is as high as 50% [8] especially in severely ill patients and those with cerebral involvement or disseminated nocardiosis and immune-suppression. Empirical combination therapy with amikacin and imipenem (or meropenem) or a three-drug regimen comprising of Sulphonamides, amikacin, and either a Carbapenem or third generation Cephalosporin can be used in such high-risk patients.

Conclusion
Isolation of nocardiae from sputum or blood occasionally represents colonization, transient infection, or contamination. In cases of respiratory tract colonization, Gramstained specimens are usually negative, and cultures are only intermittently positive. Until a better tool to determine the virulence of Nocardia is available, the positive culture often reflects disease in immune-suppressed patients, such as patients on corticosteroid therapy, patients who undergo organ transplantation, patients with chronic lung disease, and HIV-positive patients. Therefore, PN must be suspected in patients with these risk factors and positive imaging findings. Early detection of the organism can lead to the prompt initiation of treatment and reduced mortality in these patients. Initial combination therapy with two or more active agents is recommended for patients with disseminated or severe nocardiosis.

Additional Points
Learning Objectives. (i) To recognize the importance of Nocardia in causing lung infections. (ii) To diagnose Nocardia in the laboratory. (iii) To treat infections caused by Nocardia.

Post-Test
(1) How to Diagnose Pulmonary Nocardiosis? Direct demonstration of Nocardia from clinical samples stained with Gram's stain and the modified acid fast stain will help in the diagnosis of Nocardiosis. Nocardia appears as Grampositive filamentous branching rods with beaded appearance on Gram's staining and acid fast branching filamentous rods with beaded appearance on modified Ziehl-Neelsen staining. The diagnosis can further be confirmed by culturing the organism in solid media.
(2) How Can It Be Treated Effectively? Trimethoprimsulfamethoxazole (TMP-SMX) is the mainstay of treatment. However, monotherapy may lead to treatment failures. Hence, empirical combination therapy with amikacin and