(BPT) - Gastroenteritis affects millions around the world every year, according to the Centers for Disease Control and Prevention (CDC), and can be caused by viruses, bacteria and parasites, with bacteria often causing the most severe illness. Many cases don't require gastrointestinal testing, but for some, being able to distinguish between the causes of gastroenteritis is imperative in order to provide the most effective treatment for the situation. Knowing when to get tested, and what sort of test to receive, such as fast and accurate polymerase chain reaction (PCR) tests, can help you find the right therapeutic option as quickly as possible.