Narrator: This is Science Today. Immigrants from developing countries often become sick when visiting their countries of birth. According to Marylynn Yates, a professor of environmental microbiology at the University of California, Riverside, the cause of sickness is usually from drinking contaminated water.
Yates: Some microorganisms, once you're exposed to the organism, you actually develop a lifelong immunity. Other organisms, it's very short-lived and so you can be exposed to it, get sick, have a very short-term immunity, be exposed to it again and get sick again.
Narrator: Yates says the children of immigrants who were born in developed countries are most vulnerable to sickness because they have never been exposed to contaminated drinking supplies. Yates' tip – drink bottled water when traveling in countries where you are unsure of the water quality.
Yates: If you don't have the immunity or if you've lost the immunity, you will very likely get ill if you're exposed to those organisms. So, you do have to exercise common sense.
Narrator: For Science Today, I'm Larissa Branin.