Stammen was also supposedly "under the weather" but was asked today (postgame) if he had strep and he insisted he doesn't. I don't fully believe him.
From Nationals Journal in the Post:
Stammen has felt sick, having come down with the same fever Bryce Harper is fighting. But Stammen said the illness has nothing to do with his performance. After reviewing his performance, he picked up a mechanical flaw.
In other words, strep is running rampant through the clubhouse.