Too many cats to one litter box may increase their infectious illness risks.
Diseases such as feline infectious peritonitis (FIP) can be transmitted via saliva, feaces, or urine.
The more cats there are using one litter box, the higher their potential exposure. This can be particularly problematic for cats who are younger than 24 months or who have weak immune systems.
Provide multiple boxes and regularly disinfect common areas if you have a multi-kitty home.