Pneumococcal Disease Outbreak at a State Prison, Alabama, USA, September 1–October 10, 20181

S treptococcus pneumoniae (pneumococcus) causes a spectrum of disease ranging from mild respiratory infections to severe disease, including meningitis, sepsis, and pneumonia (1). Invasive pneumococcal disease (IPD) occurs when pneumococcus invades normally sterile sites. Pneumococcus is transmitted person-to-person primarily through respiratory droplets and is a leading cause of vaccine-preventable illness and death (2). Pneumococcal colonization is a precursor to disease but does not always result in disease (3). Pneumococcal conjugate vaccine (PCV) is highly effective in preventing pneumonia in adults (4), and pneumococcal disease incidence has declined since the introduction of PCV (5). IPD outbreaks are rare but can occur in settings with close personto-person contact, such as homeless shelters (6) and healthcare facilities, in which underlying conditions can increase disease risk (7).