Three Degrees Help Drive Antibiotic Decision in Cellulitis

Three Degrees Help Drive Antibiotics in Cellulitis

By: M. ALEXANDER OTTO, Family Practice News Digital Network

SAN FRANCISCO – A greater than 3° C difference in skin temperature between affected and unaffected limbs in cellulitis – measured using inexpensive, handheld, infrared laser thermometers – was found to signal the need for hospital admission for intravenous antibiotics.

Skin temperature changes in cellulitis had never been quantified, said Dr. Michael Montalto. "We’ve never had a concept in absolute terms of the differences we feel as clinicians every day. [Our study gives] an idea of the kind of scale that might cause you to think the patient needs to have an admission for IV therapy. At least in our study, if the temperature difference [between the affected and unaffected limb] was above 3 °C, those people were getting IV therapy," he said at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy.

Of 63 cellulitis patients who were admitted to the hospital for intravenous antibiotic therapy, lesions were on average 3.4 °C warmer (95% confidence interval, 3.0-3.9) than the corresponding location on the unaffected limb. The difference dropped to an average 2.1° C warmer (95% CI, 1.7-2.6) at discharge after a mean stay of 5 days, the investigators found.

Patients in the study, who were 50 years old on average, had mostly lower-limb cellulitis; just over half were men. Nurses took the limb temperatures to keep researchers blinded to the results until the study’s end. Skin temperatures did not correlate with blood pressure, core temperature, or other variables.

Dr. Montalto and his colleagues found that the warmest point on limbs affected by cellulitis dropped from an average of 34.4 °C on the day of admission for intravenous antibiotics to 32° C when patients were well enough to be discharged on oral antibiotics, a statistically significant difference (95% CI, 1.9-3.0).

Furthermore, the results also suggested a role for laser thermometers – which can cost less than $50 at electronic stores and until now have been used mostly for industrial purposes – to measure severity and treatment response in cellulitis, said Dr. Montalto, a hospitalist at Epworth Hospital and Royal Melbourne Hospital. The devices emit two beams that are focused into one dot on the skin, at which point the temperature is read from a screen. The process is quick and painless.

The thermometers are "another tool to use for tricky patients when you are wondering whether or not they are getting better," he said. Current measures – white cell counts, erythema, fever, and skin color, among others – are not specific enough, he said.

The next step in the project is to see if skin temperature helps identify the causative organism in cellulitis, which remains unknown in many cases. Methicillin-resistant Staphylococcus aureus (MRSA) cellulitis, for instance, may project a higher temperature than other types of cellulitis.

"We often have people presenting from nursing homes who don’t have a wound. They just have a big, fat, painful, red leg with nothing to swab. You’ve got no way of determining what the organism is except trial and error. If we could show that the temperature profile helps with that," and, thus, appropriate antibiotic selection, it would be a significant advance, Dr. Montalto said at the meeting, which was sponsored by the American Society for Microbiology.

True to the point, 12 patients (19%) had positive swabs in the study, mostly for staphylococci, but a few MRSA and gram-negative bacteria also showed up.

Dr. Montalto said that he had no relevant financial disclosures.

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