I'm always been quite impressed by how clean Japan is. It's definitely culturally ingrained. Imagine being the first to encounter Europeans back in the early modern period. Back when we white folk bathed once every few months if that. Even at the time, the Japanese stressed bathing as a daily ritual.
An interesting tidbit is that classical and medieval Europeans also bathed often. Most towns and cities had a communal bath house. Keeping clean was a major part of social life at the time. It only went out of style in the early modern era, when officials began to suspect that bathing spread disease. Plato probably smelled better than Machiavelli.
Anyway, with the Chinese, I tend to find a north/south divide on how clean they are. Southerners taking it less seriously. Your typical "dirty" Chinatown is mainly populated by Cantonese speakers. A lot of the new diseases from that country also seem to originate in the southern provinces. China also still has a large rural peasantry. Many of who come to the city looking for work, carrying illness spread by animals. Things have improved drastically in the major cities but the PRC needs to focus on rural sanitation and modernization. China's sanitation systems are still in rough shape. Such so that the PRC really goes out of their way to pressure citizens not to talk about how bad the toilets are. It's a major embarrassment for the communists.
Then there's India. This is a country where almost two thirds of their population has no access to closed toilets. That's not just modern flush toilets, but traditional outhouses and latrines as well. So they practise open deification, which means going out in to the middle of your field and laying a fudge pie right on the ground. Imagine every person in the United States having to do this, then double it. This results in disease, poisoning of the water supply, and even contributes to the rape epidemic. Women who go out in the fields to do their business are often attacked. More people have access to mobile phones than they do the john. There's also issues like disposing bodies in the Ganges, where people bathe. As overpopulation trends ramp up, these problems will become amplified.