SEATTLE – Lowering the Centers for Disease Control and Prevention’s temperature requirement for influenza-like illness from 100º F to 99º F would likely pick up more cases of true influenza in the emergency department, according to researchers at Rush University Medical Center in Chicago.
At Rush, 203 emergency department (ED) patients tested positive for the virus by polymerase chain reaction (PCR) during the 2012-2013 flu season, but only 135 (67%) were identified as having flu-like illness by the ED’s automated surveillance system, which pulls together provider notes, vital signs, and other information from the electronic records system in real time to identify patients with influenza-like illness (ILI), among other conditions.
On chart review, 29 (43%) of the 68 missed cases met the CDC’s requirements for ILI diagnosis: a temperature of at least 100º F, plus cough and/or sore throat. Most likely, the surveillance system was confused by double-negatives in provider notes or similar problems; Rush investigators are looking into the problem.
Dr. Marilyn Hallock
However, 39 patients with PCR-confirmed influenza did not meet the CDC’s criteria in the ED; in 15 patients (40%) it was because they had a temperature at or above 99º F, but below the 100º F benchmark.
"If you relabeled the fever criteria to greater than or equal to 99 degrees, you would actually pick up more patients. Your sensitivity would be greater, but we don’t know what would happen to the specificity. We haven’t reprogrammed the surveillance system yet to try it," Dr. Marilyn Hallock, an attending physician in the Rush ED, said a the annual meeting of the American College of Emergency Physicians. It’s something "we might want to explore further," she noted.
In the meantime, "I’m going to think twice before I say patients who come in with that gray-zone temperature between of 99º F and 100 º F don’t have influenza; they might," she said.
The rest of the 39 patients were missed for various reasons. A few arrived in respiratory distress or another condition that precluded an accurate history, while others may not have recalled ILI symptoms or were not asked about them. A number of patients were diagnosed on hospital admission from the ED when more thorough histories were taken, or when they developed the CDC triad after admission.
Dr. Hallock suspects viral PCRs were ordered in the ED for the 39 patients – although they didn’t meet CDC criteria – because it was flu season, and they complained of other flu symptoms such as myalgia and aches. "It was probably just a constellation of symptoms that led physicians to give the test," even though the patients’ ED temperatures were below 100 º F, she said.
In addition to perhaps lowering the ILI requirement to 99 º F, the investigators plan to review ILI symptoms with ED staff and work to improve their documentation, said Dr. Hallock, who indicated that she had no relevant disclosures.