How bad is Cryptosporidium?

I'm curious to know just how severe an infection with Cryptosporidium can be. Is it a mild illness that can be easily treated at home, or is it something that requires medical attention and can potentially lead to more serious health complications? Additionally, are there any specific groups of people, such as children or the elderly, who are more vulnerable to the effects of this parasite? Understanding the potential severity and impact of Cryptosporidium infections is important in order to take the necessary precautions to prevent them.