Pneumococcal disease is caused by Streptococcus pneumoniae, a bacterium that has more than 100 serotypes. Most serotypes can cause disease, but only a few produce the majority of cases of invasive pneumococcal disease.
The pneumococci bacteria are spread from person to person by droplets in the air. The pneumococci bacteria are common inhabitants of the human respiratory tract. They may be isolated from the nasopharynx of 5%–90% of healthy people.
Pneumococcal disease can be invasive, meaning a normally sterile part of the body is infected, or non-invasive. There are two major clinical syndromes of invasive pneumococcal disease: bacteremia (blood stream infection), and meningitis (infection of the meninges that surround the brain). They are both caused by infection with the same bacteria, but produce different signs and symptoms.
Pneumococcal pneumonia is a common disease caused by pneumococcal infection. Symptoms include abrupt onset of fever, shaking chills or rigors, chest pain, cough, shortness of breath, rapid breathing and heart rate, and weakness. The case-fatality rate is 5%–7% and is higher in adults 65 years and older and people with certain underlying medical conditions.
Pneumococcal pneumonia can occur in combination with bacteremia and/or meningitis (invasive pneumococcal pneumonia), or it can occur alone (non-invasive pneumococcal pneumonia). Before the COVID-19 pandemic, at least 100,000 people were hospitalized each year for pneumococcal pneumonia. At least 30,000 people were hospitalized each year for invasive pneumococcal disease, and about 3,000 people died. Rates of pneumococcal disease declined during the COVID-19 pandemic, but rates have begun to return to pre-pandemic levels.
About 4,000 cases of pneumococcal bacteremia without pneumonia occur each year in the United States. Bacteremia is the most common clinical presentation among children less than two years, accounting for up to 70% of invasive disease in this age group. The overall case-fatality rate of pneumococcal bacteremia is about 20% and may be as high as 60% among older adults.
Pneumococci cause 50% of all cases of bacterial meningitis in the United States. There are an estimated 2,000 cases of pneumococcal meningitis each year. Symptoms and signs may include headache, tiredness, vomiting, irritability, fever, seizures, and coma. The case-fatality rate of pneumococcal meningitis is about 8% among children and 22% among adults. Permanent neurological damage is common among survivors.
Pneumococcal disease is a serious disease that causes much sickness and death. Before the dip in pneumococcal disease observed in the first two years of the COVID-19 pandemic (when measures to control COVID-19 reduced the incidence of several infectious diseases), an estimated 30,000 cases and 3,000 deaths from invasive pneumococcal diseases (bacteremia and meningitis) occurred in the United States. Children younger than age two years and adults age 50 years and older have the highest incidence of serious disease. Case-fatality rates are highest for pneumococcal meningitis and bacteremia, and the highest mortality occurs among older adults and patients who have underlying medical conditions.