From an RCA press release:
Based upon a careful study of the available halachic and scientific literature, as well as a review of sanctioned practice by numerous reliable Torah authorities past and present, it is the position of the RCA that the requirement of Metzitzah is fulfilled completely and unambiguously by the use of oral suctioning through a tube, as practiced by many mohelim in our communities. Therefore, according to this viewpoint, the use of such a tube is not only permissible, but is preferred (instead of direct oral contact) to eliminate any unintentional communication of infectious diseases. This protects both the mohel and the newly circumcised child.
An additional reason to encourage the use of a tube to fulfill the requirements of Metzitzah is that we not discourage less committed Jewish men and women from observing ritual circumcision (and possibly other Jewish rituals). Indeed, even some authorities who otherwise require Metzitzah be’Peh via direct oral contact, sanction a tube if that is the only way that the parents of a child would observe the mitzvah of Bris Milah.
In light of the above, the RCA urges its member rabbis, their congregants, synagogues and institutions, as well as the larger Jewish community, to encourage and where possible necessitate, that Metzitzah be’Peh be fulfilled via a tube.