It was so, that after they had carried it about, the hand of Yahweh was against the city with a very great confusion: and he struck the men of the city, both small and great; and tumors broke out on them.
The Hebrew word translated "broke out" occurs only here in the Old Testament (1 Samuel 5:9). The Septuagint translators interpreted it accurately as "groin." These tumors were apparently most prominent in the groin area, hence the English translation "hemorrhoids." Tumors in the groin are a symptom of bubonic plague. Since the Philistines associated mice with this plague (1 Samuel 6:4-5), and mice carry bubonic plague, it seems clear that the hand of Yahweh sent this particular affliction on them.