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Avoiding Cross Contamination in the IVF Lab

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What can embryologists learn from livestock studies? Get an inside look at Dr. Kimball Pomeroy’s upcoming discussion at the Southwest Embryology Summit.

In the mid-1990s, microbial cross contamination became a hot topic after a bone marrow bag apparently leaked inside a liquid nitrogen tank, contaminating the liquid nitrogen and other bone marrow samples stored inside. As a result, six transplant patients treated at a British hospital contracted Hepatitis B from the infected bone marrow. The incident, though isolated, sparked a larger conversation about the dangers of microbial cross contamination during the shipping and storage of cryopreserved materials.

On Monday, Dr. Kimball Pomeroy plans to explore how cross contamination relates to assisted reproduction during a talk titled “microbial cross contamination during storage in liquid nitrogen – what can livestock teach us?” His talk will be part of the brand new Southwest Embryology Summit in Las Vegas. It will be geared toward embryologists who work in fertility clinics across the southwestern U.S. I chatted with Pomeroy to get a preview of his presentation.

Cryogal: What is cross contamination as it relates to storage in liquid nitrogen?

Kimball Pomeroy: Cross contamination refers to a bacteria or virus on one reproductive sample escaping from its container, getting into a nearby container and infecting another tissue that was not previously contaminated with the virus or bacteria.

Cryogal: Why is microbial cross contamination in liquid nitrogen of interest to scientists at fertility clinics?

K.P.: Eggs, embryos and semen are stored in liquid nitrogen or nitrogen vapor during shipping and storage.

Cryogal: Why use animal studies as a reference?

K.P.: There’s so much more information. We’ve been working with eggs, embryos and semen with livestock for a much longer time than with humans . . . They have taken [cow] embryos and exposed them to bacteria and viruses and transferred them into other cows and checked to see if the cows became infected and the offspring became infected. There are experiments you just can’t do on humans to test these theories out.

Cryogal: What can livestock teach us about cross contamination of reproductive specimen in liquid nitrogen?

K.P.: When we look through all the records of animal species, for example cattle species where there have been millions of vials of semen frozen, there is no history of cross contamination using the containers or tissues we use. There is a particular virus, Bovine Viral Diarrhea Virus or BVDV [a virus that suppresses the cow’s immune system.] The virus is found quite often all through the cattle industry, and it can have a big impact on the health of your herd. Yet there is not one instance we know of where there has been cross contamination when they have used semen stored in tanks where it could have been exposed to BVDV.

Cryogal: What does the (human) IVF industry do to prevent cross contamination?

K.P.: I think the biggest thing done is screening of patients. We screen our patients for sexually-transmitted diseases. A lot of the time cross contamination is not an issue mainly because the tissue we recover has almost no blood whatsoever. We also dilute out these tissues many times as we’re using different drops.

Cryogal: What else do you expect your audience to discuss?

K.P.: I’m sure a large part of the discussion is going to be on open and closed containers for storing tissue. With open containers, tissue is exposed to liquid nitrogen, and that increases the risk of cross contamination but it’s never been shown to happen . . . The alternative is a closed system, where there is, unfortunately, an insulated area of air around that piece of tissue that slows down the cooling and warming rates, but it protects it [the tissue] from being contaminated by liquid nitrogen. Liquid nitrogen is not purified. Whatever is in liquid nitrogen theoretically could contaminate the tissue.

Cryogal: Is storage in liquid nitrogen vapor preferable when it comes to reducing the risk of cross contamination?

K.P.: One of the big movements for a while was: People were looking at vapor storage tanks for storing large amounts of tissue. There are a lot of people that question whether those methods are going to be suitable, especially for vitrified specimen. They may be fine for slow-cooled specimen. Will they be able to keep vitrified specimens at the proper temperature? Do they actually remove the risk of cross contamination? I don’t think either of those has been adequately shown.


What: Discussion on microbial cross contamination
Presenter: Kimball Pomeroy, laboratory director and co-owner of Arizona Reproductive Medicine Specialists in Phoenix, Arizona. Read his bio here.
When: 2-3 p.m. Pacific Standard Time, Monday, Jan. 9, 2012
Where: Mandalay Bay Resort and Casino, Las Vegas, Nevada
Open to: Registered Southwest Embryology Summit attendees (registration is full)
More info: