Cause of recent TASS outbreak unknown

Teams of investigators are searching for the source of a recent outbreak of toxic anterior segment syndrome (TASS) following cataract surgery that has been reported in sites throughout North America since March. The current increased incidence in the occurrence of TASS appears to be unrelated to an outbreak that occurred last fall, which was linked to endotoxin contamination in the balanced salt solution (BSS) product (Endosol, Cytosol Ophthalmics/Advanced Medical Optics).

Dr. Mamalis' lab, the Intermountain Ocular Research Center at the University of Utah, is one of several laboratories working closely together to analyze this and other outbreaks of TASS and postoperative endophthalmitis.

Identifying the source is a complex task, since the potential causes of TASS are very broad. When an outbreak is seen at a single center or with a single surgeon, investigators look closely at all potential etiologies, including solutions being used during surgery, medications put into the eye, cleaning and sterilization methods for instruments, surgical techniques, implants, and phaco machines, Dr. Mamalis said.

However, the widespread nature of the current outbreak alters the usual investigational approach.

"It would be very unlikely that all of these cases that are suddenly popping up all over North America would be due to a problem with how the surgeons are sterilizing or cleaning their instruments or what detergent they are using," Dr. Mamalis said. "A common factor is triggering what is going on at the moment."

Possible causes of outbreak

"Right now we're looking very carefully at potential sources that could cause a widespread outbreak," Dr. Mamalis said. "These would include the BSS but also any of the viscoelastics that are being used, the IOLs that are being used, and the phaco machines that are being used."

The quest to identify the cause or causes of the current outbreak means enlisting as many experts as possible.

In addition to the Utah laboratory, those involved with the investigation include Henry Edelhauser, PhD, from Emory University in Atlanta as well as the Centers for Disease Control and Prevention (CDC), the FDA, and company representatives.

The CDC first worked with the ophthalmology community on last fall's outbreak and resumed the relationship when an increasing volume of calls about TASS arose this spring, said Arjun Srinivasan, MD, a medical epidemiologist at the CDC.

"It's a very complicated type of investigation to try to conduct, and that's why it needs so many groups looking at it from all sorts of different angles," Dr. Srinivasan said.

CDC, FDA efforts

The CDC and FDA, in particular, are trying to determine what investigators should be looking for when testing products that could be related to the TASS outbreak, he added.