Which stat?

I have data on prevalance of a viral infection in a population. The data is organised by age (18, 18-30, 31-50, ove5 50). I have the number of infected and non infected individuals in each category.

I would like to:
1. know if there is a statistically significant difference between the categories (if possible also which of the categories if any is statistically significantly different from the res).

2. determine if there are any trends in the data. i.e for exmaple if the infection rate increases with age.

Thank you for your help.

Regards