X-rays show predictive power for SARS

March 23, 2005

Chest radiography played a key role in early diagnoses of suspected severe acute respiratory syndrome (SARS) during the high-profile spring 2003 epidemic. Now researchers from Hong Kong have shown that x-rays also have a good chance of predicting whether SARS patients will live or die.

Chest radiography played a key role in early diagnoses of suspected severe acute respiratory syndrome (SARS) during the high-profile spring 2003 epidemic. Now researchers from Hong Kong have shown that x-rays also have a good chance of predicting whether SARS patients will live or die.

Though the threat of SARS has receded, health officials cannot rule out a fresh outbreak. Over 8400 people worldwide contracted the highly contagious disease between November 2002 and June 2003. More than 800 of these cases proved fatal.

Given the speed with which any future epidemic could spread, development of a reliable, easy-to-use prognostic indicator could prove valuable. Such a tool could guide treatment decisions and allocation of resources, according to Dr. Gregory Antonio and colleagues from the Chinese University of Hong Kong, and Hong Kong Hospital Authority, writing in the March issue of AJR [2005;184:743-741].

"If patients could be stratified according to risk early in their illness, different arms of a treatment protocol could be devised and individual treatment could be tailored," the researchers said.

They may have identified such a method. A retrospective review of patients admitted with SARS to the Prince of Wales Hospital in Hong Kong revealed that chest x-rays taken seven days after symptomatic onset to monitor disease progress could predict the likelihood of death.

"To our knowledge, this is the first study of serial chest radiographic scores to evaluate for an independent, early prognostic indicator of fatal outcome in infectious pneumonia," the report said.

The researchers examined radiographic records for 313 SARS patients from presentation until death or discharge. They analyzed the percentage area of lung opacification (AO%) and the number of lung zones affected, allocating radiographic scores accordingly. Univariate logistical regression models for these scores for each of the first 12 days after symptom onset showed day seven to be the earliest point at which reliable prognosis could be made. In practice, however, the AO% calculation could be dropped.

"Simply by scoring the number of zones affected by day seven from symptom onset, one may obtain a prediction of fatal outcome for patients," the report said. "In fact, this crude assessment is more discriminatory than using a more precise, but more subjective, AO% score. This simplification makes this scoring adaptable for real-time clinical use where its effect, in terms of suggesting change in treatment due to a rise in the odds of death, could be realized."

The authors acknowledge that confirmation of the findings will require a prospective independent study.

For more information from the Diagnostic Imaging archives:

SARS legacy lingers in Southeast Asia

AOSR seeks to broaden appeal of congress plans

PACS and mobile CT scanner tackle SARS in Singapore

Asian radiologists come to grips with SARS