I’m sure that’s a contributing factor to rapid disease spread there too. If you don’t have a healthy respiratory system you’re more susceptible to respiratory infections.
Combine that with cramped spaces and subpar sanitation and you’ve got a pandemic factory.
The disease can quickly spread do to the close quarters and a larger number of people are susceptible to it due to respiratory damage from pollution, then the disease can quickly evolve to be extremely infectious.
The problems of pollution and disease are not mutually exclusive.