Lyme disease — typically caused by the bite of an infected tick, carrying the bacterium Borrelia burgdorferi — is actually far more prevalent than we once thought. According to a new Centers for Disease Control and Prevention (CDC) report this summer, the number of Lyme cases in the U.S. is actually 10 times higher than what was originally assumed. And now CDC researchers are looking into several cases that occurred this year: sudden deaths linked to the Lyme bacteria.

“This is not a new phenomenon,” Dr. Joseph D. Forrester, a CDC scientist and one of the paper’s authors, told The Boston Globe. “However, given the severity of what happened and the tragedy of three young people to die suddenly, it was very important to investigate these cases.”

One of the victims, a Massachusetts man who was an organ donor, died while in his car. The New England Organ Bank donated his heart to CryoLife Inc., where a pathology examination occurred. Dr. Thadeus Schulz, who was examining his heart, found that there was a pattern of inflammation around the blood vessels in his heart that were similar to hearts from people with Lyme disease.

“We were curious: There was no history of Lyme disease, no characteristic rash,” Dr. Gregory Ray, medical director of CryoLife, told The Globe. But CDC tests later showed that the man had recently been infected with the Lyme disease-causing bacteria. Months later, Dr. Ray found another heart that exhibited similar features, and discovered that the patient also had had a Lyme disease diagnosis. Then there was a third with a similar case: a person in Connecticut who had dropped dead and who was confirmed to have been infected with Lyme bacteria.

The CDC is continuing to investigate the issue, as more research is needed to fully understand the link between Lyme disease and a heart condition. Lyme disease can affect the heart by causing heart block — though this may be rare, it is cause for concern. According to the CDC, about one percent of Lyme disease cases have also reported serious heart block.

Meanwhile, Dr. Stanley Plotkin of the University of Pennsylvania told The Globe that there is an “urgent” need for a vaccine against Lyme, as his son had collapsed while walking his dog and was then taken to the hospital and diagnosed with Lyme. His son was given antibiotics and a pacemaker. “I think it is unconscionable and a discredit to all parties — public health, manufacturers, Lyme activists — that no Lyme vaccine is available to humans while there is one for dogs,” Dr. Plotkin said in an email to The Globe.

Earlier this summer, the CDC released a press report that the number of people in the U.S. diagnosed with Lyme disease was around 300,000. “We know people can prevent tick bites through steps like using repellants and tick checks,” Dr. Lyle R. Peterson, director of CDC’s Division of Vector-Borne Diseases, said in a news release. “We need to move to a broader approach to tick reduction, involving entire communities, to combat this public health problem.” People who are infected with Lyme disease will typically experience fever, headache, fatigue, and a skin rash called erythema migrans — and if the disease is left untreated, the infection can spread to the heart, the nervous system, and the joints.

The CDC recommends for people to prevent Lyme disease by checking for ticks, wearing repellant, and showering quickly after being outdoors.