A CD4 count of under _______ is associated with the onset of opportunistic infections.

A CD4 count of under 200 is significant because it indicates a severely weakened immune system, making individuals much more susceptible to opportunistic infections. CD4 cells, primarily known as T-helper cells, play a crucial role in coordinating the immune response. When the count drops below this threshold, the body's ability to defend against infections, particularly those not commonly seen in individuals with healthy immune systems, becomes compromised.

Opportunistic infections can include diseases caused by organisms such as Pneumocystis pneumonia, tuberculosis, or certain types of fungal infections, which often do not harm individuals with intact immune systems. The specific cutoff of 200 CD4 cells/mm³ has been established through clinical research and guidelines, making it a key parameter in monitoring the health of individuals living with HIV/AIDS and determining treatment interventions.

The other count thresholds, while relevant, do not indicate the same level of risk for opportunistic infections. A CD4 count below 150 or higher does not align with the established clinical significance regarding the immediate risk of opportunistic infections, highlighting the importance of the 200 mark.