My son came back from mom's with lice

Not even a heads up text. Just dropped him off and I'm combing nits out of his hair that night. I had to treat the whole house, his stuffed animals, everything. When I texted her about it (trying to stay calm), she said "I didn't notice." How do I bring up hygiene/health stuff without sounding accusatory? This isn't the first time something like this has happened.