Doctors say it is important for people to be aware of the early signs of viruses and bacterial respiratory infections before a typical winter spike in cases.

They say the cold weather and indoor holiday gatherings make it easy to spread illnesses.

"Close spaces and minimal ventilation – that's kind of a perfect storm for anything that spread via an aerosolized way," says Dr. Joseph Khabbaza, a pulmonologist with the Cleveland Clinic.

Health officials say when a virus or bacterial infection becomes severe, it can develop into pneumonia. Annually, it leads to 1 million hospitalizations and more than 50,000 deaths, according to officials.

Doctors say bacterial illnesses and viruses, such the flu, are common causes of lung infections. A sign of a lung infection is chest pain when breathing or coughing. If the coughing continues, additional signs include fatigue, confusion, fever and chills.

People who are most at risk for developing severe lung infections are those 65 and older and children 5 years old and younger.

Those who suffer from chronic medical conditions such as heart disease, liver disease, lung disease, diabetes or have weakened immune systems are at risk as well.

Khabbaza recommends people who are high risk to prioritize prevention.

"There is one vaccine for the most common and deadliest kind of bacterial pneumonia, which is called streptococcal pneumonia," he says.

Anyone with bacterial pneumonia should start antibiotics as soon as possible.