English to Russian Medical Medical (general) Симптомы дифтерии (статья из медицинского журнала)

The risk of developing chronic infection with hepatitis B depends on the age at which infection occurs. About 90% of infants infected before 1 year of age, 25% to 50% of children infected at 1 to 5 years of age, 20% to 30% of older children, and 3% to 10% of adults become carriers. People of any age with -underlying health problems- that affect their immune system are also more likely to become carriers.

В Большом англо-русском медицинском словаре (Акжигитова) написано:
underlying condition ~ 2. основное заболевание 3. сопутствующее заболевание (?)

Заранее спасибо!