A spike in cases of a bacteria infection that can cause pneumonia is being seen in countries around the world and is believed to be the cause of a spike in infections in an Ohio county.

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While an increase of pneumonia cases have been seen in Ohio, Massachusetts, China and Denmark, health officials say those cases aren’t connected to a “new or novel” virus, but to a bacteria that is well-known to health officials.

According to the Centers for Disease Control and Prevention, the illness, seen often in children, is caused by a bacteria called mycoplasma pneumoniae. While the result of an infection with M. pneumoniae is typically a mild respiratory infection, the illness can progress to a more serious respiratory disease.

A spike in cases of the infection has been seen in Warren County, Ohio, where public health officials say 145 children have been diagnosed with M. pneumoniae infections.

“There have been no reported deaths,” the Warren County Health District said in a statement. “While the number of cases is higher this year, the severity is similar to previous years. Most cases recover at home and are treated with antibiotics.”

In addition to the cases being seen in Ohio, Massachusetts is also reporting an outbreak of “walking pneumonia,” or milder pneumonia infection cases in children.

M. pneumoniae has also been spreading in China and has reached epidemic levels in Denmark. Researchers from Denmark’s Statens Serum Institute have said an increase in M. pneumoniae cases began during the summer. The country has seen a spike particularly in the past five weeks, according to Forbes. More than 540 cases were reported last week alone.

World Health Organization officials reported during a health conference in November that there has been an uptick in respiratory illnesses in China since mid-October, though they reiterated that the illness does not appear to be linked to a novel virus.

China’s health ministry said the surge in cases in the country has been caused by the flu and other known pathogens and not by a novel virus.

M. pneumoniae infections happen mostly in late summer and fall, according to the CDC.

The most common type of infection that comes from M. pneumoniae is tracheobronchitis (chest cold), and the most common symptoms of a chest cold include:

• Sore throat
• Feeling tired
• Fever
• Slowly worsening cough that can last for weeks or months
• Headache

Children younger than 5 years old who get M. pneumoniae infections could have symptoms that are different from older children and adults, the CDC says. Instead, they may have the following cold-like symptoms:

• Sneezing
• Stuffy or runny nose
• Sore throat
• Watery eyes
• Wheezing
• Vomiting
• Diarrhea

Symptoms typically last for a few days but can stretch for more than a month, according to public health officials.