McKeown said doctors and “everybody who needed to know” were notified in early January. Health officials didn’t want to alarm the public, she said.

“It’s a difficult balancing act to decide between creating concern among the public and being very transparent,” she said. “We decided that with 44 patients, it was important for the people of Wisconsin to know what was going on even if we don’t have all of the answers yet.”

Five disease investigators from the CDC joined state health investigators last month in interviewing affected patients and families and gathering samples that might help pinpoint the source.

The investigators have been visiting homes, nursing homes and other nursing facilities, Braden said. Samples are being collected for testing from water, drains, skin care and personal care products, over-the-counter medications and medicines distributed by pharmacies, he said.

The 44 patients are on different water systems, with some using wells, so the source doesn’t appear to be a water distribution system, Braden said.

The Wisconsin State Laboratory of Hygiene, part of UW-Madison, has been testing patient samples and collecting environmental samples to ship to the CDC, said David Warshauer, the lab’s deputy director of communicable diseases.