They may have been quarantined in the hospital on what was day two of the outbreak however as things got worse that system would break down and as visitors to Savaana they would most likely go back to the hotel (a place they know).
Remember three months is a long time, so in any investigation you start with what you know,
They were at the Marsh House Hotel, from the reception you could find out which room and grab a spare key.
Inside the room could be a digital camara with view screen so they can see all the photos of where they went or one of the parents diary's?
From this information they would plan their next move on which location to choose or a person to look out for.
Also although implied Clem's farther was attacked by a crazy person, they didn't say bitten so it could have been a regular attacker (human) and maybe alive