bailau - the group in question was not fully vaccinated, so they were still at risk of contracting the virus. With packed planes and airports (especially STT!!), travel seems the logical place the virus might be contracted, hence the negative results on arrival and positive on day 4. Most false positives are tied to rapid tests not full PCR (at least my experience here with friends and associates) and BVI is doing full PCR testing. When we visited last month we went in with eyes wide open, knowing all the potential risks, including possible Q and inability to return back to US if, somehow, we contracted COVID there. We should be fully vaccinated before our return trip mid June, and while modified restrictions for fully vaccinated travelers would be welcome, we're not counting on it and again will insure for, and plan for, the risks.