A quick refresher on the types of germs that can cause infection or disease.

By Stephanie Abramson
Unless you grew up during the Black Death and thus believe that your coworkers are in danger of sneezing out their souls, saying “Bless you” is more of a charming courtesy than a social requirement. And courtesy requires that you balance reality against adherence to tradition. In other words, if every time someone sneezes, you yell “Bless you” across the office, and she yells “Thank you,” and you yell “You're welcome,” then the pendulum may be tipping away from graciousness and toward irritating interruption. “Blessing” someone has the paradoxical effect of drawing negative attention to the sneezing—especially if “Bless you” is (passive-aggressive) code for “Thanks for getting us all sick.” That said, I like to say “Bless you” when people sneeze, and I like people to say it to me. It’s a dangerous world, and I’ll take all the kindness I can get. So if you’re talking about the odd nearby achoo—not bouts of serial sneezing—go ahead and offer a whispered blessing or gesundheit. Or, you know, a tissue.
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  • Viruses: Microorganisms that invade living cells and need a host to survive and replicate. Viruses are responsible for many diseases that have no known cure, like the common cold and stomach flu. Antiviral drugs, like Tamiflu, which treats influenza, are difficult to develop, and few exist.
  • Bacteria: Tiny single-cell life forms that reproduce easily. Bacteria live in food and water and can survive on humans, too. Strep throat and E. coli are examples of bacterial infections.
  • Parasites: Organisms that live in or off a host, feeding off its tissues and fluids. Giardia, a common parasitic infection in the United States, spreads through contaminated drinking water and can cause diarrhea and cramps.
  • Fungi: Organisms, including yeasts, that can live in air, water, soil, and plants. Fungi can cause irritating infections and allergies, such as candida and athlete’s foot.