This is a jukugo word that uses the on'yomi readings of the kanji. You haven't learned this reading for 赤 yet, so here's a mnemonic to help you:
You know what dysentery isn't? Sexy (せき). That's right. If anyone tries to seduce you by saying they have dysentery and they'd like to share it with you, tell them how NOT sexy that is and get the heck away from them!
The dysentery bacteria was detected in five men and women total.