I don't know how public health operates in India but I can share some information on how it is in the US.
First off, though, look at Mother Teresa. She operated under the Order (of nuns) she was with, ultimately worked for the Vatican, I guess.
So the religious route is one you could take.
In secular public health, it is governments that run Public Health programs, as far as I know.
PHN's (Public Health Nurses) do the following, at least where I worked. It might be different somewhat in other
run TB clinics
run STD clinics
run vaccination clinics
run Prenatal clinics
run Pediatric clinics
do home visits re: Failure to Thrive, Lead poisoning, High Risk Pregnancy, domestic violence, child abuse, Gastrointestinal Infections (like Salmonella, Giardia, and other infections, and trace the infections to their source, then follow up with contacts to make sure contacts are treated;
In Public Health, the patient is not the individual, it is the community. For example, if a worker at a restaurant has a contagious illness,
the procedure is to require the worker to stop working and receive medical care for the infectious disease. Being out of work lasts until
the worker is free of contagion. You would have the somewhat unpleasant and difficult task of requiring the worker to lose income while
you are protecting the public. And you would also be finding out if any customers were affected by the infected worker.
Same with contacts of active TB patients, those with gonorrhea, syphilis, and other STD's.
Someone who is taken off of work can apply for unemployment or maybe welfare benefits.
You might be involved in community groups that deal with alcoholism, you might work with schools, police, correctional facilities, or businesses that are wanting help with basic hygiene or other issues about which a nurse would be knowledgeable.
Best wishes, I hope this helps.