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Normal-Looking Radiographs Can Delay Pneumonia Diagnosis

Many clinical guidelines recommend chest x-rays when pneumonia is suspected in adults. A new study, which looked at pneumonia cases that developed during the 2009 H1N1 influenza pandemic, suggests that this screening tool may not always be accurate enough, especially in detecting the early interstitial stage. Find out what the authors recommend when the initial radiograph looks normal but symptoms suggest otherwise...

Chest x-rays miss nearly half of early-stage pneumonia cases associated with influenza, according to a study recently published in Critical Care. In 34 pneumonia patients who presented to Italian EDs with influenza-like illness (ILI) and acute respiratory distress during the 2009 pandemic, initial radiography failed to detect pneumonia in 16 cases (47% of the time). Bedside chest ultrasonography (US), however, correctly identified 15 of those 16 cases when done nearly simultaneously with x-rays.

Researchers initially looked at 98 consecutive patients with suspected 2009 pandemic (H1N1) infection who complained of ILI or severe acute respiratory illness at triage. Patients who had no signs of respiratory distress and those with co-morbidities were excluded from the study. In 41 patients, a final diagnosis of community-acquired pneumonia (CAP) was confirmed and chest ultrasonography was done on 34, of which 16 had normal initial chest x-rays and 18 had abnormal radiographic findings.

Of the 16, two-thirds had a final diagnosis of viral (H1N1) CAP, 5 had primary bacterial pneumonia, and 1 had secondary bacterial pneumonia. In 15 of the 16 patients, initial US detected interstitial syndrome. US also found alveolar consolidation, pleural effusion, or pleural line abnormalities in 11 of those patients. US failed to identify 1 case of confirmed pneumonia in the abnormal chest x-ray group and 1 in the normal x-ray group. US also detected interstitial syndrome in 5 of 33 controls, which researchers suggest could be related to (H1N1) infection based on its prevalence in the community during the study period.

Researchers reported that CAP patients with initially normal chest x-rays were more likely to have viral (H1N1) pneumonia compared to those with abnormal radiography and to be earlier in the disease progression. As a result, bedside chest US could help emergency physicians rapidly identify patients who should start treatment for pneumonia. In particular, a US interstitial pattern with spared areas is strongly predictive of viral pneumonia. As influenza A (H1N1) can rapidly progress to severe illness, leading to ICU admission or death, early detection and initiation of antiviral treatment can reduce disease severity and associated mortality.

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