A farmer with chest pain and lung nodules

TYPICAL FEATURES OF BRUCELLOSIS

Brucellosis is a zoonotic disease transmitted to humans not only by ingestion of infected dairy products, but also by direct contact with infected animals or by inhalation of contaminated aerosols. This latter physiopathologic mechanism of acquiring the disease seems to be the most probable when the lungs are involved, ¹ and it is common in people such as our patient, whose occupation exposes them to Brucella species.

Although brucellosis can initially present with mild respiratory tract symptoms, true pulmonary involvement (characterized by a more aggressive and prolonged course) is very uncommon, with a reported incidence of 1% to 7%.^1,2 Respiratory involvement in brucellosis may appear as part of a systemic illness, as the presenting symptom of the disease, or even as a solitary abnormality on chest radiography.¹ Bronchopneumonia, interstitial pneumonia, empyema, pleural effusion, paratracheal lymphadenopathy, and lung nodules have all been reported.²

Reinfection or a late relapse?

In our patient, a question was whether the second episode of brucellosis was a reinfection or a late relapse of the disease. Reinfection seemed the most feasible explanation, supported by his continuous occupational exposure, the properly treated first episode (rifampicin 600 mg daily and doxycycline 100 mg twice daily, both for 45 days), the long symptom-free period, and the fact that most relapses have been reported to occur during the first 6 months after therapy.³ However, late reactivation of an asymptomatic chronic lung infection was also possible, given the ability of Brucella species to survive inside the phagocytic mononuclear cells; brucellosis reactivation has been reported even 28 years after the first episode.⁴

DIAGNOSTIC CHALLENGES

The diagnosis of brucellosis with laboratory testing is challenging. The organism is difficult to isolate in sputum culture (only one case has been described until now),⁵ and serologic tests can be falsely negative, although this is rare.^6,7 In fact, serologic testing in patients with focal brucellosis may be falsely negative when the serum agglutination test is performed,^4,7 as could have occurred in our patient. In several studies, pleural fluid culture has been shown as a good method to isolate Brucella organisms,⁸ but biopsy is often the only way to establish the diagnosis.⁶

Complications of lung involvement in brucellosis are seldom severe and, when they appear, usually respond to the same treatment as for uncomplicated brucellosis.²

The combination of respiratory symptoms, epidemiologic risk factors, an endemic setting, and a history of a previous episode all raise clinical suspicion of brucellosis. If clinical suspicion is high, negative results of sputum, serology, or pleural fluid cultures should never rule out the disease; biopsy of the respiratory region affected is warranted.