Final answer:
The most likely underlying cause of non-bilious vomiting and diarrhea is a gastrointestinal infection, particularly viral gastroenteritis, with norovirus being a common culprit especially in the context of regional outbreaks.
Step-by-step explanation:
Possible Underlying Causes of Non-Bilious Vomiting and Diarrhea
In cases where a patient experiences non-bilious vomiting and diarrhea, the most likely underlying cause is an infection or intoxication of the gastrointestinal (GI) tract. The absence of bile in the vomit suggests that the issue may be located above the bile ducts in the digestive system, such as the stomach or upper intestines. The acute gastroenteritis-like symptoms, including vomiting and diarrhea without blood in the stool, point to a gastrointestinal infection as the primary reason for the patient's symptoms.
Common pathogens associated with such symptoms include viral agents like norovirus and rotavirus, and less commonly bacterial pathogens such as Campylobacter jejuni or enteropathogenic Escherichia coli (EPEC). Considering the scenario of multiple cases appearing in a region, a viral cause such as norovirus, which is highly contagious and often encountered in outbreaks, is most plausible. Treatment for such conditions typically involves rehydration therapy and supportive care, as antibiotics are not effective against viruses.
While a definitive diagnosis would require laboratory tests and a detailed patient history, the clinical presentation aligns closely with viral gastroenteritis, especially given the seasonal spike in cases consistent with an outbreak. Hence, viral gastroenteritis would be the leading differential diagnosis in this clinical scenario.