From what I understand it is more of an issue with what they call the lady boys and the lack of condom use among young people in general. I dont plan an on engaging in hedonistic sexual activities like a 20 year old. I lived through the Aids epidemic during my 20s in the 1980s and was quite active, I am not the least bit concerned now.
But yes, diseases are a concern there. I am more concerned about mosquitoes and the various things that they carry. But life is not without risk and I find the risk acceptable.
We are talking about Sea Kraits, one of the most venomous species of snakes. Kind of a blue-tinged white and black stripes. Small fangs in the back of the mouth. I’ve heard they come up on land at night but I’m not sure that’s true.
I’ve heard that you can grab one by the tail end and squeeze it from tail to head, forcing the air out of its lungs so it will immediately rise to the surface for a breath. Not something I want to try.
For people shooting underwater video, I recently learned of an amazing app to improve quality and color: Aquacolorfix.
Someone get these MFing snakes out of my MFing thread! 
I guess We were blissfully unaware of the danger we were seeing, just thought they were kind of neat. We were actually far away from them since we were snorkeling and they were snaking along the bottom; the guide had to point them out to us. That and there was a lot of other things going on like coral, sponges, fish and actual natives diving from their little boats.
What really amazed us were the giant clams. OMFG they were cool. A guide went down and petted one and it moved and seemed to change color. It was one of the most awesome things I have ever seen.
The snakes are not dangerous to humans. I’ve had the snorkeling habit for a long time and I’ve never heard of a human being bitten. My bane is larval jellyfish, also known as Sea Lice. They leave a bite that’s just as annoying and itchy as a bedbug bite. Diclofenac sodium 1% gel helps tremendously. They seem to pick on me more than almost anyone else, and I have to wear a rashguard suit and gloves to protect myself.
The giant clam interior colors are different bright neon shades, eh? Amazing, indeed.
Did you go to a Marine Sanctuary to snorkel, or are regular reefs that good in your area? Around here one needs to go to a Marine Sanctuary for the best experience.
There’s a guy on YouTube who calls himself The Critter Hunter. His videos, which mosty feature tiny bottom dwellers, are worth watching.
There’s a band composed of expats in the Philippines, which you will find on Youtube, called The Dogs of Wah. I like most of their material quite a lot, and you probably will as well. My favorites are I’m Falling Apart and It Is What It Is.
Expats are generally more friendly than folks in the US. I have more friends in the Philippines than in the US. There is a fairly high proportion of Trumpers and conspiracy theorists, but enough of them are regular humans to make it socially rewarding.
We went to the Giant Clam Sanctuary next to the Pearl Farm Resort on Samal island. It was a guide tour with lifevest and a guide that pulled you around. There must have been a hundreds of Giant Clams, I was not expecting that.
We also went to an reef on the southern tip of Samal Island. Very clean and distant from Davao City, not a sanctuary but very nice. It only cost like $200 for us both to do on the same trip. Which I thought was a great deal considering we had the boat and the guide to ourselves.
Here at Dauis Panglao (DP) Island there are 2 sanctuaries immediately offshore. One has a shoal of sardines that’s fun to swim in and around plus Tuna and other assorted fish and coral. The othe has assorted fish and corals and a number of Giant Clams.
There are 2 more sanctuaries that each need a half hour boat ride to get to. They have assorted fish and corals and feature Sea Turtles, most of which are 4 to 5 feet long.
BTW if you are caught touching living coral or a Sea Turtle it will be a Very Large Fine for you. A photo that someone took and posted on social media will be enough to convict you.