The Church does not oppose multiple sexual partners because monogamy has a lower risk of infection.
The Church opposes multiple partner sex because it’s against natural law. Sex is not for fun but for procreation in the context of a couple who will commit, love and care for the child and each other. There would be NO infection if everyone or almost everyone followed natural law and the Church teachings. HIV for example would never have evolved to spread sexually from the initial infections of man in those remote African villages where people slaughtered chimpanzees and became infected from their blood. These people then instead of infecting only their wives and stopping the infection there infected many more people and spread the disease. Increasing urbanisation and ease of transport increased this further, but people in monogamous relationships would at best infect only one person and no-one else. Each case of HIV would be a dead end for the HIV.
So the posting of this sort of thing is irrelevant to catholic teaching. Oral sex beween people who have been tested for infection and proved negative, or who use barriers is also oppose by the Church.
It is not irrelevant. In fact it is most relevant. Casual sex has created an evolutionary and ecological niche for the spread of infectious particles because people just can’t keep it in their pants and casual sex is considered moral as long as it is consensual. Listening to the Church teaching would have avoided creating that niche or eliminated it when it was present from previous times.
I imagine that people who attend crowded churches also have higher rates of influenza transmission, especially in the third world, and in Catholic services attended by many children.
Irrelevant because crowded attendance can happen just as much with secular functions. Influenza et al. are also usually not as deadly and can be contracted at the post office, government office, shopping mall and one’s regular secular humanist meeting.
Besides one can increase ventilation and sunshine and reduce risk of pathogen spread tremendously. UV light from the sun and fresh air either inactivates infectious particles or disperses them to such a degree that they’re no longer infectious. Hand washing also cuts down on transmission. The Church also does not command people not celebrate open masses or not ventilate the church premises or wash hands after shaking them with others after mass before eating.
Remember sexually transmitted diseases such as ano-rectal carcinoma, cervical carcinoma, vaginal carcinoma, HIV/AIDS, pelvic inflammatory disease, syphilis and so on are diseases of lifestyle. It should be said that there are other lifestyle diseases such as diabetes, hypertension, coronary heart disease, stroke, gout, osteoarthritis, elevated cholesterol levels, different types of cancer, etc. could also be avoided in many cases with a more rigorous approach to Christian teachings.