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 weakened 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]

History

Although there is not international data available on worldwide infection rates per year, there are roughly 500-1000 documented cases of nocardiosis a year. Most of these cases occur in men, as there is a 3:1 ratio of male of female cases a year; however, this difference may be based on exposure frequency rather than susceptibility differences. From an age perspective, it is not highly more prevalent in one age group than another.^[4] Cutaneous Nocardiosis is slightly more common in middle aged men, but as a whole, all ages are susceptible.^[5] Additionally, there is no racial basis when it comes to becoming infected with Nocardiosis.

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.^[6]

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.

A weakened immune system is a general indicator of someone who is more susceptible to nocardiosis, such as someone who already has a disease that weakens their immune system. Additionally, those with low T-cell counts or other complications involving T-cells can expect to have a higher chance of becoming infected. Besides those with weak immune systems, a local traumatic inoculation can cause nocardiosis, specifically the cutaneous, lymphocutaneous, and subcutaneous forms of the disease.^[4][7]

Signs and 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^[8][9]

Cardiac conditions

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

Lymphocutaneous disease

• Nocardial cellulitis is akin to erysipelas but is less acute
• Nodular lymphangeitis mimics sporotrichosis with multiple nodules alongside a lymphatic pathway
• Chronic subcutaneous infection is a rare complication and osteitis may ensue
• May be misidentified and treated for as a staph infection, specifically superficial skin infections^[10]
• Cultures must sit more than 48 hours to guarantee an accurate test

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 of nocardiosis can be done by a doctor using various techniques. These techniques include, but are not limited to: a chest x-rays of the lung, a bronchoscopy, a brain/lung/skin biopsy, or a sputum culture.

However, diagnosis may be difficult. Nocardiae are gram positive weakly acid-fast branching rod-shaped bacteria 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.^[11] Infiltration and pleural effusion are usually seen via x-ray.

Treatment

Nocardiosis requires at least 6 months of treatment, preferably with trimethoprim/sulfamethoxazole or high doses of sulfonamides. In patients who do not 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.^[11]

Prognosis

The prognosis of nocardiosis is highly variable. The state of the host's health, where the infection is, duration of the infection, and how severe the infection is all play parts in determining the prognosis. As of now, skin and soft tissue infections have a 100% cure rate, and a pleuropulmonary infections have a 90% cure rate with appropriate therapy. The cure rate falls to 63% with those infected with dissemented nocardiosis, with only half of those surviving infections that cause brain abscess.>. Additionally, 44% of people who are infected in the spinal cord/brain die, and is increased to 85% if that person has an already weakened immune system. Unfortunately, there is not a preventative to nocardiosis. The only recommendation is protect open wounds to limit access.

References