This image comes from "Microbiological laboratory hazard of bearded men," a peer-reviewed research paper concerning the risk bearded scientists who work with bacteria and viruses might pose to their families. Published in 1967, the study tested whether bearded men were more likely to accidentally "carry" microbes home with them.
You can read the whole study online. And thank God for that. Because it's full of more great out-of-context quotes than I have time to cut and paste today.
Conclusion: Dirty hippie scientists shouldn't normally be a threat to family and friends. However, accidental beard-based contamination is possible, if the bearded scientist in question does a lot of repetitive, close-contact work with microbes. (Read: Grad students) In which case, those scientists should really wash their beards before they leave the lab.
Thanks, David Ng!