Nocardiosis

Nocardiosis is an infectious disease affecting either the lungs (pulmonary nocardiosis) or the whole body (systemic nocardiosis). It is due to infection by bacterium of the genus Nocardia, most commonly Nocardia asteroides or Nocardia brasiliensis.

It is most common in men, especially those with a compromised immune system. In patients with brain infection, mortality exceeds 80%; in other forms, mortality is 50%, even with appropriate therapy.^[1]

It is one of several conditions that have been called the great imitator.^[2]

Cutaneous nocardiosis commonly occurs in immunocompetent hosts.^[3]

Causes

Normally found in soil, these organisms cause occasional sporadic disease in humans and animals throughout the world. Another well publicized find is that of Nocardia as an oral microflora. Nocardia spp. have been reported in the normal gingiva and periodontal pockets along with other species such as Actinomyces, Arthromyces and Streptomyces spp.^[4]

The usual mode of transmission is inhalation of organisms suspended in dust. Another very common method is that by traumatic introduction, especially in the jaw. This leads to the entrance of Nocardia into the blood stream and the propagation of its pathogenic effects. Transmission by direct inoculation through puncture wounds or abrasions is less common.^[1] Generally, nocardial infection requires some degree of immune suppression.

Symptoms

Pulmonary Infection

• Produces a virulent form of pneumonia (progressive)
• night sweats, fever, cough, chest pain
• Pulmonary nocardiosis is subacute in onset and refractory to standard antibiotherapy
• symptoms are more severe in immunocompromised individuals
• radiologic studies show multiple pulmonary infiltrates with tendency to central necrosis

Neurological Infection

• Headache, lethargy, confusion, seizures, sudden onset of neurological deficit
• CT scan shows cerebral abscess
• Nocardial meningitis is difficult to diagnose

^{[5] [6]} Cardiac Conditions

• Nocardia has been highly linked to endocarditis as a main symptom
• In recorded cases, it has caused damage to heart valves whether natural or prosthetic

Lymphocutaneous disease

• Nocardial cellulitis is akin to erysipela but is less acute
• Nodular lymphangeitis mimics sporotrichosis with multiple nodules alongside a lymphatic pathway
• Mycetoma is a rare complication and osteitis may ensue

Ocular disease

• Very rarely nocardiae cause keratitis
• Generally there is a history of ocular trauma

Disseminated nocardiosis

• Dissemination occurs through the spreading enzymes possessed by the bacteria
• Disseminated infection can occur in very immunocompromised patients
• It generally involves both lungs and brain
• Fever, moderate or very high can be seen
• Multiple cavitating pulmonary infiltrates develop
• Cerebral abscesses arise later
• Cutaneous lesions are very rarely seen
• If untreated, the prognosis is poor for this form of disease

Diagnosis

Diagnosis may be difficult. Nocardiae are weakly acid-fast organisms and can be visualized by a modified Ziehl-Neelsen stain like Fite-Faraco method In the clinical laboratory, routine cultures may be held for insufficient time to grow nocardiae, and referral to a reference laboratory may be needed for species identification.^[7] Infiltration and pleural effusion are usually seen via x-ray.

Treatment

Nocardiosis requires at least 6 months of treatment, preferably with co-trimoxazole or high doses of sulfonamides. In patients who don’t respond to sulfonamide treatment, other drugs, such as ampicillin, erythromycin, or minocycline, may be added.

Treatment also includes surgical drainage of abscesses and excision of necrotic tissue. The acute phase requires complete bed rest; as the patient improves, activity can increase.^[1]

A new combination drug therapy (sulfonamide, ceftriaxone, and amikacin) has also shown promise.^[7]

References