State health officials have confirmed three new cases of Legionnaires’ disease linked to the ongoing Hopkins outbreak, bringing the total number to 20, including one death.

In all the cases, including the three announced Tuesday, patients were exposed to the bacteria in the Hopkins area before Sep. 9. Since then, health officials have taken steps to eliminate possible infection sources; cooling towers on several local businesses were disinfected and a decorative fountain was shut down.

State investigators said last week that they expected the number of cases to grow, but crucially the new cases do not represent disease exposure that happened after remediation steps were taken. It can take up to 10 days for Legionnaires’ symptoms to develop, and even then, reporting to state officials can be delayed because some who are infected do not seek treatment immediately.

Legionnaires’ disease is contracted by inhaling mist or aerosolized water droplets that contain the Legionella bacteria. Symptoms include cough, fever and difficulty breathing. In its most severe form, the disease results in a pneumonia that can be fatal to those with compromised immune systems or chronic diseases.

Of the 20 cases, 16 people were sick enough to require hospitalization. The average age of those infected is 59, but at least one case occurred in someone in their late 20s.

Health Department investigators are still trying to identify how the outbreak started, agency spokesman Doug Schultz said. “We continue to investigate potential sources of the outbreak,” Schultz said. “None has been confirmed nor ruled out at this point.”

While a “few” cases developed in people who visited Hopkins, Schultz said, most cases occurred in people who live or work in the Minneapolis suburb. Disease investigators are interviewing victims, sometimes more than once, in an effort to track their movements and identify a common source.