What are the possible causes and how to verify Mass Diarrhoea?

What are the possible causes and how to verify if there is a mass diarrhoea while all food tested negative for salmonella, S.Aureus and E.coli.

There are roughly 600 microbes that can cause diarrhea. It depends on what the other symptoms are 

Diarrhoea is a very common symptom of food poising, so you'll need others sypmtoms as Scampi suggested, and other info if available i.e. common foods, locations etc to narrow it down.

Do you have any more information than "mass diarhhoea" :rolleyes:

There are also viruses that can cause it.

"Mass Diarrhoea" always reminds me of a local pub that got closed by Environmental Health for a while - a customer was ill with what turned out to be norovirus, but in the attempt to clean up the vomit the business managed to inadvertently aerosolise it, and caused a fairly significant localised outbreak...

other than diarrhoea, 22 person have other random symptoms like 1 or 2 have fever, 5 to 6 have vomit, 1 to 2 nausea.

19 have 1 common food prior to onset. no other common area include food history up to 72 hours before the suspected meal, lodging, etc.

the suspected food tested negative for salmonella, S.Aureus and E.coli.

suspecting Rotavirus but awaiting stool test of food handlers.

Any other special experience that you could share?

You really need to relay this to your local public health!!!

What is the common ingested food/drink between all people that had diarrhea? 

Perhaps depending on Location, Cholera is of course another frequent suspect if "food" includes water.

A common cause - hygiene breakdown.

Verification - visual / micro.

Then again, many schools are well aware of C.perfringens.

Easier to open a book on foodborne diseases.