Sampling techniques for checking community spread of covid

Hi…my question is, there are random samples that need to be taken to check if there is community spread of covid…A) how do we ascertain how many samples need to be taken…meaning 20 or 30 or more etc…do we use infection rate and population count as a base? Or something else. B) in this situation how do we get unbiased sample…meaning with all the travel restrictions wouldn’t we be taking samples only from a given city, state or just hospitals??? After collecting what ever data we have how do we ensure there is No bias and if there is, can we do anything to correct it?

Hi @amitsati,
Yes the population density should be a parameter while sampling the data, there can be numerous criterions based on what the statistician’s choice.
For unbiased sampling, i think travel restrictions have nothing to do with it, as the samples can also be taken from the perspective places