Michigan teenager Rylie Whitten, 15, thought she had the flu.

Then her family noticed her sunburn-like rash. A few days later, Rylie was in the hospital being treated for a severe case of toxic shock syndrome (TSS), The Daily News reported.

Rylie is one of several recent cases of TSS in the state. Over the last three months, the Michigan Department of Health and Human Services (MDHHS) has recorded more cases of TSS than it has in any given year over the past decade.

Since December 2015 the MDHHS has identified five cases, concentrated in Kent County, of the bacterial illness, which often results from the improper use of tampons. For the past 10 years, there have been fewer than four cases annually statewide.

Nationwide, the incidence of TSS was decreased sharply in the 1980s—from 890 cases in 1980 to 61 in 1989—and has remained low ever since.

In a press release addressing the recent spike in TSS cases, the MDHSS warned women not to leave tampons in too long and to use the lowest absorbency needed. Whitten was reportedly using “super absorbent” tampons at the time of infection, as were three of the four other young women. An MDHHS spokesperson told The Daily Beast that all of the affected women in the past few months were between the ages of 15 and 18. None have died.

“Although Toxic Shock Syndrome cases are rare, this recent cluster is an important reminder to always review product safety information,” said Dr. Eden Wells, chief medical executive with the MDHHS.

TSS is rare, only affecting one in every 200,000 people, but it can be life-threatening. The illness results from infection with Staphylococcus aureus, which can colonize the vagina, or Streptococcus pyogenes. It causes causes a wide range of symptoms including sudden fevers over 102 degrees Fahrenheit, rash, low blood pressure, vomiting, skin peeling, muscle aches, and disorientation. If untreated, TSS can lead to multiple organ failure and death. The MDHHS notes that the national fatality rate for TSS is 4 percent of all cases.The FDA estimates that about half of TSS cases are related to tampon use, although the exact means of infection is still unclear. In this case, four of the five young women were using Playtex Sport brand tampons and one was using U by Kotex.

A spokesperson from Playtex tampons told The Daily Beast that the company “hope[s] that each young woman who has been affected by Toxic Shock Syndrome condition is able to quickly and fully recover, and feel she’s back to being her best as soon as possible.”

“Toxic Shock Syndrome is a rare but serious condition, and we share the Michigan Department of Health and Human Services’ commitment to ensuring that women are informed about appropriate and safe tampon use,” the spokesperson added, noting that the company’s tampons meet both FDA regulations and internal safety standards.

A spokesperson for Kimberly-Clark, which owns Kotex, told The Daily Beast that “our hearts go out to all of the young women and their families in western Michigan that have been dealing with TSS.”

“Nothing is more important to Kotex than the safety and effectiveness of our products and the well-being of the consumers who use them,” Kotex said. “Our tampons have to meet exacting safety and quality measures in our manufacturing process and we are proud of our long track record of producing safe and effective Kotex products.”

At the height of the TSS public health panic, the CDC identified an association between the absorbency of tampons and the occurrence of TSS, prompting manufacturers to reduce the absorbency of their products. In 1982, the FDA required tampon packages to include warnings that women should use the lowest absorbency necessary and, by 1990, the federal agency had standardized measurements like “super” and “super plus” across brands.

The FDA told The Daily Beast that it is looking into these latest TSS cases.

“FDA is aware of the increase in TSS cases linked to tampon use and has been working with Michigan state health authorities to learn more about the recent cases,” a spokesperson said in a statement. “The agency recommends that women read and follow the instructions on tampon package labels to minimize their risk of TSS and to understand the warning signs.”

The exact association between high-absorbency tampons and TSS, as the FDA notes, is unclear. High-absorbency tampons can cause vaginal dryness and ulcerations that some researchers suspect serve as a “portal of entry” for the offending bacteria. But the precise nature of that link is unknown.

At the moment, all the pertinent agencies are reluctant to blame the cases on any specific brand or product.“We’re still looking for an association,” Brian Hartl of the Kent County Health Department told a local NBC affiliate. “We aren’t ready to go forth and say this brand of tampons caused this because you can understand the implications of doing that.”

Rylie Whitten, meanwhile, is back at home and at school, lucky to be alive.

Update 3/4/16 2:45 PM: This story was updated to add comment from Playtex Sport.