Final answer:
A cross-sectional study would be the best study design for investigating the given scenario of COVID-19 outpatients diagnosed between 22 and 28 March. This design allows for the collection of data from a specific group of people at a specific point in time, which can provide valuable insights into the characteristics and patterns of the disease.
Step-by-step explanation:
The best study design that can be used for investigating the given scenario would be a cross-sectional study. This study design involves collecting data from a specific group of people (outpatients diagnosed with COVID-19 between 22 and 28 March) at a specific point in time. By conducting interviews with a randomly selected sample of patients, epidemiologists can gather information about their symptoms, risk factors, and potential sources of exposure to understand the patterns and characteristics of the disease within this population.