Diagnosis

Identifying hospitalized patients with SARS is difficult, especially when no epidemiological link has been recognized and the presentation of symptoms is non-specific. Patients with SARS might develop symptoms common to hospitalized patients (e.g., fever or prodromal symptoms of headache, malaise, and myalgia), and diagnostic testing to detect cases is limited (MMWR 52: 547-50). Unless specific laboratory tests (PCR, detection of SARS antibodies; see Chapter 7: Diagnostic Tests) confirm the initial suspicion of SARS infection, the diagnosis of SARS is based on the clinical findings of an atypical pneumonia not attributed to any other cause, as well as a history of exposure to a suspect or probable case of SARS, or to their respiratory secretions or other body fluids.

As mentioned above, during the early stages, SARS may be difficult to differentiate from other viral infections, especially when symptoms are unspecific (Rainer). The initial diagnostic testing for suspected SARS patients should include chest radiography, pulse oximetry, bacterial cultures of blood, sputum, and urine, serology for mycoplasma, chlamydia, influenza, parainfluenza, respiratory syncytial and adenoviruses, nasopharyngeal aspirates for viral cell cultures, and direct sputum smear for Pneumocystis jiroveci by silver stain. A specimen for Legionella and pneumococcal urinary antigen testing should also be considered (CDC, http://www.cdc.gov/ncidod/sars/diagnosis.htm).

The radiographic appearance of peripheral air-space opacities is indistinguishable from other causes of atypical pneumonia, such as Mycoplasma, Chlamydia, and Legionella, and overlaps with other types of viral pneumonia. The presence of an air-space opacity on chest radiographs has been helpful in the confirmation of the diagnosis (Wong 2003b).

Clinicians should save any available clinical specimens (respiratory, blood, and serum) for additional testing until a specific diagnosis is made. Acute and convalescent (greater than 21 days after the onset of symptoms) serum samples should be collected from each patient who meets the definition criteria for SARS. Specific instructions for collecting specimens from suspected SARS patients are available on the Internet: http://SARSreference.com/link.php?id=19