Dear Reader: Some schools in my district are facing an outbreak of norovirus like you wouldn't believe. Why is it spreading so fast? What can I do to protect our family?

Dear Reader: Norovirus, which has earned the nickname "the vomiting bug," is extremely contagious. Add stomach cramps, fever, diarrhea and muscle pain to the list of symptoms and you get a good sense of the misery it causes.

It's the leading cause of gastrointestinal illness in the United States. About 21 million people get norovirus each year. Up to 70,000 of those land in the hospital, and about 800 die. And calling norovirus an "it" is misleading. There are actually many different types of norovirus, so getting sick with one kind doesn't offer protection from others.

The virus is shed in the feces of an infected individual. That means when someone with norovirus follows poor hygiene after a bowel movement, they spread it to everything that they touch. You can pick up norovirus by eating or drinking something handled by a contaminated person, by touching a contaminated surface and later putting your fingers in your mouth, or through close contact with someone who is sick. The virus is also present in a sick person's vomit, which adds another layer of risk when caring for sick children.

One of the reasons that outbreaks are so difficult to contain is that the norovirus is a hardy organism. It's impervious to hot and cold and to many disinfectants. When the virus gains a foothold in crowded and self-contained places like a school, hospital, nursing home or cruise ship, it spreads quickly.

Upping the ante is the fact that it can take up to a week for the norovirus that's already in your body to make you feel sick. And once your symptoms have ended, the virus can be found in your stool for more than two weeks.

So what do you do when norovirus hits nearby? Keep in mind that just because a neighboring school is affected, that doesn't automatically mean your child's will be as well. That said, there are several steps you can take to lessen the risk of infection.

-- All family members should wash their hands often. Use soap and running water and scrub for at least 20 seconds. Always wash after using the bathroom and before preparing food.

-- Carefully wash all fruits, vegetables and seafood before preparing them. Most outbreaks spread in food service areas, so when a norovirus outbreak is nearby, it's not a bad idea for your child to bring her own lunch and snacks to school for the duration.

-- Explain to your kids how the virus is transmitted. That will help them understand these rules: no fingers in the mouth (always a good idea at any time), and no sharing food or drinks with anyone, even if they don't look sick.

-- If someone in the house does become ill, use a bleach-based disinfectant to clean any surfaces contaminated by vomit or diarrhea. Don't forget door and drawer knobs, the fridge and the TV remotes.

-- If you're the one who's sick, don't prepare, cook or serve food for others.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I am recovering from a bout of diverticulitis. What are my chances of having another round -- and how can I avoid later episodes? Does the onset increase my risk of serious ailments such as cancer?

Dear Reader: Diverticula are sac-like protrusions from the colon wall. If you were to look inside the colon, diverticula would appear as holes within the colon wall, leading to a bulging sac coming from the intestine. In the United States, diverticula almost always occur near the end of the colon in an area called the sigmoid colon. Chronic pressure in this area from poor intestinal motility, or contractions, leads to the formation of these outcroppings. Diverticula are quite common in the Western world. In one set of screening colonoscopies -- conducted in 624 patients with an average age of 54 -- 42 percent had diverticula. Note that the likelihood of diverticula increases with age.

The presence of diverticula is known as diverticulosis. Inflammation of the diverticula is known as diverticulitis. The latter occurs when increased pressure within a diverticulum leads to a perforation through which bacteria leave the intestine, causing infection. The infection can become so severe that an abscess develops.

Diverticulitis is more prevalent among people with a low-fiber, high-fat diet that includes a lot of red meat. It is also more common among people who are obese, have little physical activity and smoke cigarettes. A common myth, and one I learned in medical school, was that nuts, seeds, corn or popcorn could become trapped in a diverticulum and lead to diverticulitis. A 2008 study not only disproved this myth, it found that the opposite was true among men ages 40 to 75.

A first-time episode of diverticulitis can mimic many of the same symptoms as colon cancer. So unless you've had a colonoscopy in the last year, you should rule out cancer by having a colonoscopy, preferably six to eight weeks after a bout of diverticulitis. One study found that 2.8 percent of people who had a follow-up colonoscopy were then diagnosed with colon cancer. This rate rises for those who have had an abscess related to diverticulitis.

After the first attack of diverticulitis, the likelihood of a second attack is about 33 percent; the likelihood of a third bout after a second bout is also about 33 percent. To help prevent another attack, you need to get the gut moving. That is, increase fiber in your diet. If you can't do this simply by increasing your consumption of high-fiber vegetables, fruits and nuts, then a fiber supplement is in order.

Exercising also will decrease the risk of another attack of diverticulitis. Because diverticulitis occurs more frequently in obese people, losing weight may also decrease your chance of another attack. Decreasing the amount of red meat and fat in your diet may lessen your chances as well.

Nationwide, the incidence of diverticulitis is increasing, especially in people ages 18 to 44. Some of the increase could be attributed to better diagnosis, but the rise is also emblematic of our unhealthy diet and sedentary lifestyle.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: So many people are required to undergo tuberculosis screening even though they don't know anyone with TB and have no symptoms. Just how contagious is tuberculosis?

Dear Reader: Tuberculosis, or TB, is an extremely infectious and potentially life-threatening disease. One-third of the world's population is infected with TB, which causes about 1.7 million deaths each year. Infection rates in the United States are quite low by comparison, with 9,287 new cases reported in 2016.

The causative agent of TB is a rod-shaped bacterium called Mycobacterium tuberculosis. It's released into the air when an infected person sneezes, coughs, or even speaks or breathes. By breathing in these microscopic droplets, which can remain airborne for several hours, a person who comes into contact with an individual with an active TB infection can contract the disease.

Transmission of TB after brief exposure to an infected individual is rare. According to the Centers for Disease Control and Prevention, TB cannot be spread by contact with clothes, a handshake, the toilet or other surfaces.

Once the TB bacterium is inhaled, it can move through the bloodstream to other parts of the body, like the kidneys, spine or brain. However, in most cases, the bacterium affects the lungs. There, if left untreated, it can cause pockets and cavities to form. These can bleed, get infected and form abscesses, cause holes or block airways. Left untreated, TB can kill you.

You asked why even those without TB symptoms are tested. The reason is that, in most healthy people, the body's immune system is good at neutralizing the TB bacterium. It does this by forming a protective capsule, known as a granuloma, around the bacillus. Although this isolates the bacterium, it doesn't kill it. That means that the person is now a TB carrier, otherwise known as latent TB. The danger here is that the immune system can lose the upper hand at any time, and the latent infection can become active.

People with latent TB don't have symptoms and are not contagious. However, they must receive treatment to get rid of the disease. Without anti-TB drugs, active disease can develop. That risk is highest during the first few years following infection. For some people, it continues throughout their lives.

So what are the symptoms of TB?

They include a bad cough that lasts for three weeks or more; a cough that brings up blood or sputum; general weakness or fatigue; unexplained weight loss, fever, chills and night sweats.

If you have had contact with someone who has TB, or if you have several of these symptoms, particularly those involving the lungs, you should get tested. A blood or skin test will show whether the TB bacillus is present. A chest X-ray or a sputum culture will reveal active disease.

Treatment will depend on whether the disease is active or latent. Active disease is treated with several drugs taken over the course of up to six to nine months. A further complication is that some TB bacterium is drug-resistant. This requires very specific treatment by infectious disease specialists.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)