Tummy problems in the first 48hrs are usually nothing to do with bugs but more to do with the change of time zones and eating times, something that can be avoided by slowly adjusting to the time a month before so you only have 4hrs difference when you arrive
You can pick up bugs from insect bites and water, but they are difficult to avoid. What were the dishes washed in? Where did the ice come from? Teeth cleaning... tap water??? Is the bottled water from Australia as it will be safer than any from the Phil, Indonesia, etc.