Q fever pneumonia

Q fever pneumonia refers to pulmonary infection with the organism Coxiella burnetii. It is sometimes classified as an atypical pneumonia. It can occur as either sporadic or outbreak cases.

Clinical presentation

The clinical picture is often dominated by fever, headaches and myalgias ⁵. A cough, if present, is often non-productive and may even be absent despite the presence of the pneumonia.

Pathology

Coxiella burnetii is an obligate intracellular parasite (zoonosis: small gram-negative coccobacillus) that lives in the phagolysosomes of the host cells. Common animal reservoirs include goats, cattle, sheep, cats, and occasionally dogs. The organism has a worldwide prevalence.

Serology

The diagnosis can be established serologically (i.e. total antibody or IgM).

Radiographic features

Plain radiograph

The radiographic differentiation of Q fever pneumonia from other types of community-acquired pneumonias is not possible. Segmental or lobar opacification and occasional pleural effusions may be seen (all of which are non-specific features on their own). Features can be slow to clear ⁴.

CT chest

CT features are, again, individually non-specific and often confirms airspace involvement, which can be lobar, segmental, patchy or a combination thereof. Often, more than one lobe may be involved.

In the acute phase predominant CT findings are

• areas of consolidation (present on almost all cases ¹³)

• nodules (maybe present in around 2/3^rds of cases ¹³) with halos of ground-glass opacity, predominantly with segmental and peripheral distributions.

• distribution

  • lesions often affect all lobes, and predominate in the left upper and lower lobes.

  • involvement of more than one lobe was observed in many cases

Treatment and prognosis

Tetracycline is traditionally considered the drug of choice ^1,2. Chloramphenicol, cotrimoxazole, and rifampicin may also be effective. In most cases, the pneumonia results in an illness of mild-to-moderate severity, although, on occasion, it can be rapidly progressive and may result in respiratory failure ⁵.

History and etymology

In 1935, there was an outbreak of a enigmatic fever in workers in a large abattoir in Brisbane, Australia. All other causes of fever were excluded, and pending working out its actual cause, the condition was named "query" or "Q" fever by Edward H Derrick (1898-1976) ¹¹ the Director of the Laboratory of Microbiology and Pathology in the Queensland Health Department in Brisbane, Australia in 1937 ^1,10.