WRT catching a disease from the communion cup-
The Center for Disease Control says it has been answering the question for more than 20 years.
In 1998, the CDC included this statement in the American Journal of Infection Control:
For more than two decades, the Centers for Disease Control and Prevention (CDC) has stated an official position to inquirers (e.g., lay public, physicians, nurses, and other health care professionals) about the risk of infectious disease transmission from a common communion cup. Although no documented transmission of any infectious disease has ever been traced to the use of a common communion cup, a great deal of controversy surrounds this issue; the CDC still continues to receive inquiries about this topic. In this letter, the CDC strives to achieve a balance of adherence to scientific principles and respect for religious beliefs.
Within the CDC, the consensus of the National Center for Infectious Diseases and the National Center for Human Immunodeficiency Virus, Sexually Transmitted Diseases, and Tuberculosis is that a theoretic risk of transmitting infectious diseases by using a common communion cup exists, but that the risk is so small that it is undetectable. The CDC has not been called on to investigate any episodes or outbreaks of infectious diseases that have been allegedly linked to the use of a common communion cup. However, outbreaks or clusters of infection might be difficult to detect if: (1) a high prevalence of disease (e.g., infectious mononucleosis, influenza, herpes, strep throat, common cold) exists in the community, (2) diseases with oral routes of transmission have other modes of transmission (i.e., fecal-oral, hand-to-mouth/nose, airborne), (3) the length of the incubation period for the disease is such that other opportunities for exposure cannot be ruled out unequivocally, and (4) no incidence data exist for comparison purposes (i.e., the disease is not on the reportable disease list and therefore is not under public health surveillance).
Experimental studies have shown that bacteria and viruses can contaminate a common communion cup and survive despite the alcohol content of the wine. Therefore, an ill person or asymptomatic carrier drinking from the common cup could potentially expose other members of the congregation to pathogens present in saliva. Were any diseases transmitted by this practice, they most likely would be common viral illnesses, such as the common cold. However, a recent study of 681 persons found that people who receive Communion as often as daily are not at higher risk of infection compared with persons who do not receive communion or persons who do not attend Christian church services at all.
In summary, the risk for infectious disease transmission by a common communion cup is very low, and appropriate safeguards – that is, wiping the interior and exterior rim between communicants, use of care to rotate the cloth during use, and use of a clean cloth for each service – would further diminish this risk. In addition, churches may wish to consider advising their congregations that sharing the communion cup is discouraged if a person has an active respiratory infection (i.e., cold or flu) or moist or open sores on their lips (e.g., herpes).