What is one of the AIDS-defining illnesses associated with CD4 counts lower than 200?

Pneumococcal pneumonia is considered one of the AIDS-defining illnesses associated with a CD4 count lower than 200 cells/mm³. This is significant because a CD4 count below this threshold indicates a severely compromised immune system in individuals infected with HIV, leading to an increased risk of opportunistic infections.

Pneumococcal pneumonia is caused by the bacterium Streptococcus pneumoniae and presents a considerable risk in patients with advanced HIV infection. When the CD4 count drops below 200, the body loses its ability to effectively control infections, making patients particularly vulnerable to pneumonia and other infections that are typically not as threatening to immunocompetent individuals.

The other options listed do not fit the criteria for AIDS-defining illnesses. Hypertension, diabetes, and asthma are common medical conditions that can occur in individuals regardless of their HIV status and are not classified as opportunistic infections or AIDS-defining conditions. Hence, pneumococcal pneumonia's association with low CD4 counts highlights its critical role as an indicator of advanced HIV disease.