Dear Doctor: I heard about a polio outbreak in Nigeria this summer. Might there be an outbreak here in the United States?

Dear Reader: Polio is a crippling, and sometimes fatal, infectious disease that was once common in the U.S. Caused by the polio virus, the disease was widespread among children. During the 1940s and '50s, outbreaks caused spinal and respiratory paralysis in 15,000 sufferers each year. With potentially dire outcomes and no cure, polio became one of the most feared childhood diseases in the United States.

That changed thanks to the development of the polio vaccine in the mid-1950s, and to the success of our ongoing national vaccination program. The Centers for Disease Control and Prevention states that polio has been eliminated in the U.S.

In our country, vaccination programs have resulted in a sharp decline in the number of polio cases, from 35,000 in 1953 to 5,300 four years later. With the introduction of an oral vaccine in 1961, the number of new cases acquired in the U.S. continued to plummet. There have been no new cases of polio reported in the U.S. since 1979. The last known case of polio acquired outside the U.S. and imported into the country was in 1993.

However, as you point out, polio remains a global concern. International health organizations have made polio vaccination a priority, with more than 2.5 billion children vaccinated worldwide since 1988. As a result, the overall number of new polio cases worldwide has dropped a remarkable 99 percent.

In 10 countries, however, including Afghanistan, Syria and Pakistan, vaccination programs have been difficult to implement and the disease continues to spread. And though Nigeria was declared polio-free in 2014, two new cases last August and a third case in September have raised the alarm. World health organizations are now redoubling their efforts to implement ongoing vaccination programs.

Is this polio epidemic a danger to the U.S.? The answer is no. Vaccination rates among adults are extremely high, and as long as parents continue to be vigilant about vaccinations and boosters for their children, we as a nation will remain immune to this terrible disease.

According to CDC guidelines, children should be vaccinated with inactivated polio vaccine (IPV) four times -- at 2 months of age, at 4 months of age, a dose between 6 and 18 months of age, and a booster dose between 4 and 6 years of age. Until this vaccination schedule is complete, children should not travel to an area where polio is still an active infection.

Eradicating polio worldwide has been one of the most remarkable and successful international health initiatives. Its ongoing success depends on each one of us continuing to be vigilant about vaccination.

(Eve Glazier, M.D., MBA, is an internist and assistant professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and primary care physician at UCLA Health.)

Dear Doctor: Will taking acetaminophen (Tylenol) during pregnancy increase the chances that the child will have ADHD or autism?

Dear Reader: Such concern is understandable. Parents and parents-to-be have been alarmed over the past few years by two Danish studies that raise the specter of greater ADHD and autism risks among children whose mothers took the over-the-counter pain killer acetaminophen during pregnancy. But let's look at these studies a little more closely.

The largest of these studies showed that, among children whose mothers ever used acetaminophen during pregnancy, 5.7 percent showed symptoms of hyperactivity by age 7. Among children whose mothers never took acetaminophen, 4.3 percent showed symptoms of hyperactivity. Similar mild differences were also noted for emotional problems and overall conduct.

Here's the important caveat: The two groups of women were themselves very different. Participants who used acetaminophen were more likely to be smokers, more likely to be obese (BMI greater than 30) and more likely to have had a fever. Just having a fever during pregnancy has been associated with autism, behavioral abnormalities and problems with attention.

As for the autism study, it linked acetaminophen use during pregnancy to an IQ drop of 2 points in 5–year-olds. Here, the cause of the acetaminophen use is an especially important factor. In this study, 37 percent of the mothers who used acetaminophen had fever; only 23 percent of those who didn't use acetaminophen had fever. And again, those who used acetaminophen were more likely to be smokers.

So one has to ask: Why does someone take acetaminophen during pregnancy? The answer: To reduce a fever. So fever may be the problem, not the acetaminophen. Further, women who smoke and are obese are more likely to be unhealthy during pregnancy, more likely to take acetaminophen for physical problems and more likely to have children who may also be less healthy.

Would I recommend acetaminophen regularly in pregnancy for joint pain and muscle aches? Probably not, though I would take it for a fever and for moderate pain. Otherwise, it's better to do prenatal yoga, gentle stretching and maintain a good diet.

(Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.)

Dear Readers: Welcome to the second day of our new "Ask the Doctors" column. As an internist and primary care physician at UCLA Health, my approach to medicine is to understand that I don't have all the answers -- that I have to learn new topics and review old topics all the time.

Sometimes, I can provide answers right away. But sometimes, I have to stop and reassess. Medicine has seen many breakthroughs since I graduated from medical school nearly 20 years ago, and evidence has changed many dogmatic ways of practice.

Objective, non-biased data are important to the practice of medicine. Doctors must understand how that data can be applied to one person or to large groups of people.

You met my colleagues Dr. Eve Glazier and Dr. Elizabeth Ko yesterday and learned about their approach to health and wellness. My column focuses on commonsense answers based upon scientific literature. As I increase my professional knowledge, I hope to provide people with thoughtful and deliberate interpretations of medical science that people can use to direct their own health.

Dear Doctor: My job requires me to sit in front of a computer for at least eight hours a day. When I come home, I usually watch television for a few hours before going to bed. Is being so sedentary bad for me?

Dear Reader: Unequivocally, yes. Many studies of many types have found increased death rates among people who sit for prolonged periods. The biggest problem is being sedentary in front of a television.

The average American watches more than four hours of television per day. Some studies have found that for every additional two hours in front of the television, the risk of diabetes increases 14 to 20 percent.

Here's why: Sitting for prolonged periods decreases insulin sensitivity, meaning your blood sugar rises. Add to that the types of sugary foods that are often eaten while watching television, and you have the creation of a serious health problem. If you're sedentary throughout the day, exercise can help ease the negative impact, but not completely make up for it.

So for starters, watch less television or, if you do watch television, put an exercise bike in front of the screen. Second, if you have a job in which you sit for long periods, take three-minute breaks every 30 minutes to stretch and walk around a little. Every little bit of activity helps.

(Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.)