Imaging reveals unique characteristics in newest strain of bird flu

Researchers have, for the first time, detailed the pulmonary radiologic findings of the human infection of the latest subtype of avian influenza virus, and described these findings in an article published online July 2 in Radiology.

The subtype, H7N9 influenza A pneumonia, is characterized by rapidly progressive changes in the lungs and pulmonary connective tissues, ground-glass opacities (GGOs) and air bronchograms, according to Zhiyong Zhang, MD, PhD, of Shanghai Public Health Clinical Center and Shanghai Medical College of Fudan University in China, and colleagues.

“At presentation, patients with H7N9 influenza had rapidly progressing lower respiratory tract infections,” they wrote. “Imaging findings, along with clinical manifestations and physical examination and laboratory findings, help establish early diagnosis.”

The first human outbreak of H7N9 was reported in China in March. It can cause acute respiratory distress syndrome, organ failure and death, according to the researchers.

To learn more about the imaging findings associated with the virus, Zhang and colleagues reviewed clinical data and radiologic files from 12 patients with H7N9 who were admitted to the authors’ facility in April. Nine of the patients were men, and the average age was 66 years old. All patients exhibited a fever with temperatures between 100.4℉ to 104℉, as well as cough, shortness of breath, white phlegm and loss of strength. While cases of bird flu in humans are typically caused by contact with infected poultry or secretions from infected birds, most patients in the current study had no clear history of exposure to poultry.

All patients underwent chest radiography and thin-section CT as an initial exam, with chest x-rays taken every one or two days thereafter to monitor disease progression and treatment response.

This imaging revealed that all patients had GGOs, and most had consolidations, air bronchograms, and interlobular septal thickening, reported Zhang and colleagues. Some patients also had centrilobular nodules, reticulations, cystic changes, bronchial dilatation and subpleural linear opacities. Lung lesions were mostly detected in the right lower lobe, but involved at least three lobes in all patients. The severity of the imaging findings mirrored the severity of the patient’s clinical condition, according to the authors.

Zhang and colleagues wrote that the rapid progression, GGOs and consolidations with interstitial changes seen in H7N9 pneumonia may help differentiate it from other causes of pneumonia, though they stressed that the imaging patterns in the study are nonspecific.

“Although they are nonspecific, recognition of the radiologic findings will help narrow the differential diagnosis,” wrote the authors. “A specific diag­nosis of H7N9 pneumonia could not be made on the basis of imaging features alone. Combining imaging features with clinical and laboratory data can help make the early diagnosis of H7N9 infection.”