Outlander Season 6: What made Claire and Tom sick?

Neither Claire nor Tom Christie had dysentery in Outlander Season 6. What got them both sick?

After recovering from her illness, Claire could run through her symptoms. She didn't have the bloody flux.

Had it not been for Tom Christie having the same symptoms as her, it probably wouldn't have been a big deal.  

To get that information, they would have had to be in contact, but they didn't have that much contact at the time.

When Claire asked Tom for a stool sample, he refused. Did we ever learn what the cause of their illness was?

In Outlander Season 6, Claire is still not sure what caused her illne

The topic of the illness moved on very quickly after the stool sample was requested.  

Claire still doesn't know. Malva showed up accusing Jamie of having an affair and that she was carrying his child. 

When the topic of concern was an illness the two had recovered from, they couldn't talk about it.