Yesterday, my sister-in-law learned that the mohel who circumcised her three-month-old son has been accused of infecting babies with herpes. Like any mother would, she freaked out and spent the day getting her son tested. Let's take a step back and briefly examine the issue of metzitzah, ignoring the issue of this particular mohel.
The Mishnah in Shabbos (19:2; 133a) states that metzitzah must be done at the end of a circumcision. As the commentators explain, metzitzah is the sucking of a bit of blood from the circumcision wound to start its healing (the mohel then spits the blood out on a napkin). The Gemara (133b) explains that refraining from performing metzitzah is a danger for the baby.
However, contemporary science tells us that there is no danger to the baby if metzitzah is not performed. Presumably, then, there would be no need for metzitzah. I suspect that many posekim would agree to this conclusion if not for an important historical fact. One of the first changes that the Reform movement enacted was abolishing metzitzah. Because of this, there was an understandable reaction among the Orthodox to insist on maintaining the practice so as not to confirm the Heterodox (see the posts on this subject, listed on the right). Thus, throughout the nineteenth century we find extended discussion of metzitzah, neatly summarized in Sedei Hemed (ma'arekhes metzitzah) and, with historical information added, by Jacob Katz in his Divine Law in Jewish Hands.
One example of an analysis is in the Tiferes Yisrael commentary to the Mishnah (Shabbos 19:2). He accepts that the danger no longer exists and explains the different medical circumstance from the Gemara's by stating that nature has changed (nishtaneh ha-teva). However, since even doctors agree that there is a small benefit to performing metzitzah the practice should be continued.
It is interesting to note that, in Budapest, the practice of metzitzah was abolished with the approval of the rabbi of Ungvar.
For a long time, various instruments have been introduced so that the metzitzah can be done without direct contact between the mohel's mouth and the circumcision wound. Some posekim prohibited any change in the practice, mainly because it would be a confirmation of the Heterodox. We cannot change this custom even one bit. Others adopted these instruments and, by now, they have become fairly standard in non-Hasidic communities. At my oldest son's bris, I asked the mohel out of curiosity whether he would be willing to perform metzitzah be-feh (i.e. directly with the mouth, without an instrument) and he said that if I wanted it done I could do that part myself.
Interestingly, the following was written by R. Hershel Schachter in Nefesh Ha-Rav (p. 243) about R. Joseph B. Soloveitchik's position on this matter, and was confirmed by R. Fabian Schoenfeld as having happened at his son's circumcision:
Our teacher's view was that nowadays there is no need for metzitzah at all, like the Tiferes Yisrael's view in the Mishnah [sic!] (see the Sedei Hemed for a long treatment of this). He told us how a mohel once wated to perform metzitzah be-feh and our teacher asked him not to. When the mohel refused, our teacher told him that if his father, R. Moshe Soloveitchik, were there, he would definitely not have allowed him to perform metzitzah be-feh. However, I am more tolerant and since you are refusing, I will let you.