The genus Nocardia consists of aerobic actinomycetes, organisms that exhibit a fungus-like, branching growth pattern. These microbes are ubiquitous in the environment, and over 40 species are considered capable of causing disease in humans. Nocardia nova is recognized as one of the most frequently isolated species from clinical samples. Like other members of its genus, N. nova is an opportunistic pathogen, meaning it typically causes infection, known as nocardiosis, in individuals with compromised immune systems. This infection can affect various parts of the body, presenting a diagnostic and therapeutic challenge for medical professionals.
Identity and Environmental Habitat
Nocardia nova belongs to a cluster of related species often referred to as the Nocardia nova complex, which was historically part of the broader Nocardia asteroides complex. This bacterium is a Gram-positive, rod-shaped organism that frequently displays a beaded, branching filamentous structure when viewed microscopically. A key laboratory characteristic for its classification is its property of being weakly acid-fast due to the presence of shorter-chain mycolic acids in its cell wall.
The natural habitat of N. nova is widely distributed across the globe, as it functions as a saprophyte, surviving on decaying organic matter. It is commonly isolated from environmental sources, including soil, dust, and both fresh and saltwater. Human exposure typically occurs through two primary routes. The most frequent route is the inhalation of airborne bacterial particles suspended in dust, which leads to pulmonary infection. Alternatively, infection can follow traumatic inoculation, where the bacteria enter the body through cuts or scrapes exposed to contaminated soil.
Clinical Manifestations of Infection
Infection with Nocardia nova can manifest in three main forms, with the specific presentation depending on the site of entry and the patient’s immune status.
Pulmonary Nocardiosis
Pulmonary nocardiosis is the most common manifestation, typically resulting from the inhalation of the bacterium. Symptoms often progress slowly, mimicking other respiratory illnesses like tuberculosis or bacterial pneumonia, with patients presenting with fever, cough, chest pain, and weight loss. This form of the disease can lead to the formation of lung abscesses or cavitary lesions.
Primary Cutaneous Nocardiosis
This form occurs when the organism is directly introduced into the skin through trauma. It often presents as cellulitis, skin ulcers, or subcutaneous nodules, which may eventually drain purulent material. While the cutaneous form can affect anyone, it is the most common presentation in individuals who are otherwise healthy.
Disseminated Nocardiosis
This is the most serious presentation, where the initial infection spreads via the bloodstream to other organs. The central nervous system (CNS) is the most frequent site of spread, occurring in up to a third of all nocardiosis cases. CNS involvement can lead to the formation of brain abscesses, causing symptoms such as severe headache, confusion, seizures, or other sudden neurological deficits.
The risk of developing a severe infection is significantly higher for immunocompromised individuals, as N. nova is a low-virulence organism. People with underlying health conditions like HIV/AIDS, cancer, diabetes, or those receiving immunosuppressive therapies are particularly vulnerable.
Treatment and Prognosis
Diagnosing Nocardia infection is challenging because the bacteria grow slowly in laboratory cultures, sometimes requiring up to 14 days of incubation for isolation. Accurate species identification, often requiring molecular methods, is necessary because different Nocardia species exhibit varying patterns of antibiotic resistance.
Treatment requires protracted antibiotic therapy, which must be maintained for a long duration to prevent relapse. For uncomplicated infections in otherwise healthy individuals, treatment typically lasts for a minimum of six months. Patients who are immunocompromised or have CNS involvement require even longer courses of treatment, often extending to 12 months or more.
Trimethoprim-sulfamethoxazole (TMP-SMX) is generally considered the first-line antibiotic choice for nocardiosis. However, due to the increasing prevalence of species-specific resistance within the Nocardia genus, susceptibility testing is an important step to guide therapy. In cases of severe or disseminated disease, or when the patient is immunocompromised, combination therapy with two or more antibiotics, such as amikacin, linezolid, or carbapenems, may be initiated until susceptibility results are available.
The prognosis for nocardiosis varies considerably based on the site of infection and the patient’s underlying health status. For healthy patients with localized cutaneous or pulmonary infections, the outcome is generally favorable with appropriate treatment. However, the prognosis is guarded for individuals with compromised immunity or those whose infection has disseminated to the central nervous system. Fatalities can occur in a significant percentage of cases, especially when the infection involves the brain or spinal cord.