Which of the following is NOT a droplet disease?

Measles is primarily transmitted through airborne droplets rather than being classified strictly as a droplet disease. It can spread through respiratory droplets in the air and can remain infectious for a period even in the absence of a symptomatic individual in the environment. In contrast, the other diseases listed, such as mumps, whooping cough, and rubella, are primarily spread through close contact with respiratory droplets generated when an infected person coughs or sneezes. Therefore, while measles can be transmitted via droplets, it involves a broader and more sustained airborne transmission route compared to the others, which are more characteristic of droplet-borne diseases. Understanding these transmission methods is crucial for implementing appropriate infection control measures in healthcare settings.