If you read Roman history, it is clear one of the biggest killers was infection. Even those at the top of the social hierarchy like Emperor Titus or Drusus the Elder died from ailments that modern penicillin probably would have cured. In the case of Drusus, he smashed his leg in a horsefall and died from an infection of the wound. The following Septic hazard is an optional rule intended to give campaigns an added level of grit. It highlights the every day dangers of infection and will make players think twice about wading into battle. Only use it if you feel it will add something to your campaign.
Medicine Skill TN: 7 (+1 per wound)
Skills: P, M, C
This is a bacterial infection of the woud site which, if it continues to spread, enters the blood and reaches the organs. Anytime a player takes a wound that breaks the skin, assume he has been exposed to this hazard and roll 0d10 (two d10 taking the single lowest result) against his Hardiness. If the roll meets or exceeds his score then the wound becomes infected and progresses at the above rates (killing in about a week). Though Romans have no knowledge of bacteria, medical rolls made to keep the site clean and apply salves can stop the infection. However the difficulty of such rolls increases with each wound increment by +1 (starting at TN 7). So a character who takes three wounds and acquires an infection, requires a Medicine Skill Roll (TN 10) to be cured.
For further clarification of Hazards see pages 37 and 40 of the Servants of Gaius rulebook.