opportunistic infection
noun [ C ] medical specialized uk/ɒp.ə.tjuːˌnɪs.tɪk ɪnˈfek.ʃən/ us/ɑː.pɚ.tuːˌnɪs.tɪk ɪnˈfek.ʃən/
机会性感染（细菌或病毒引起的感染，对健康人一般无害，但会影响自然防御感染能力受损的人）
an infection caused by bacteria or a virus that is not harmful to a healthy person but harms a person whose body's natural defence against infection is damaged
The most common opportunistic infection associated with AIDS is a type of pneumonia.