The following are the factors for the disparity mentioned in the question.
1. Absolute amount of income- The absolute amount of income earned by the rich is very high as compared to that of the poors. Consequently, the amount spent on the health facilities by the rich is although higher than the poors (as they demand superior medical facilities), yet this amount is lesser in terms of proportionate basis.
2. Hygienic conditions- The poors usually live in slums areas, where the conditions are pretty unhygienic. On the contrast, the rich people live in well-built houses situtated in posh areas. Hence, they are less prone to most of the water-borne and infectious diseases.
3. Transportation costs- Normally, most of the modern medical facilities are available in towns and cities. This obviously forces the poors to undertake the journey to these places, hence, they have to incur the medical costs along with the transportation costs.
4. Leaves and offs-from jobs- The poors normally are engaged in the informal sector, so for them falling ill implies leaves. Often, these leaves implies either loosing of jobs or unearned days. Hence, illness adversely affects the incomes of the poors. On the other hand, richs are engaged either in well-paid formal sector or they are business-man (entrepreneurs). For rich people, taking leaves from the job doesn't necessarily implies loosing of jobs or pay-cuts.