Investigators are now seeking to establish how the funds were requested, approved, and eventually spent.
Sources familiar with the probe say detectives are examining official documents, payment records, travel details, and approval procedures.
They want to determine whether the trip to Mbale actually took place as reported, who participated, and whether the expenses declared match the services delivered.
The Christmas tree lighting ceremony has also drawn attention due to the amount of money allegedly used.
Investigators are questioning how such a large sum could have been spent on what appears to have been a simple event.
They are reviewing procurement records to see if the process followed the law and whether there was value for money.
The 22 individuals summoned are expected to record statements and provide any documents that may help clarify the situation. Failure to honour the summons could lead to further legal action.
The EACC has in recent years increased its focus on county governments, where large amounts of public funds are managed.
The commission maintains that it is committed to ensuring accountability and protecting taxpayer money from misuse.
Leaders in Bungoma County have yet to respond fully to the allegations. Some have indicated that they are ready to cooperate with investigators and provide all necessary information.