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.)

Dear Doctor: What are the benefits of oregano oil?

Dear Reader: Oregano is well-known for its culinary versatility -- I like it with pasta and in chimichurri sauce -- but it has purported health benefits as well. A native of the Mediterranean region, the plant was used by the ancient Greek physician Hippocrates as an antiseptic and as an aid for digestive and respiratory ailments.

The beneficial effects of oregano appear to be from two specific chemical compounds, carvacrol and thymol. Both have been shown to have activity against multiple bacteria in laboratory settings. Among the many subspecies of oregano, all of them contain these two compounds -- known as phenols -- in some proportion. Oregano contains other phenol compounds as well, potentially boosting its antibacterial effects.

These compounds could be at least part of the reason why both the oregano plant and oregano oil inhibit the replication of intestinal pathogenic bacteria, such as Escherichia coli, Bacillus cereus and Salmonella, as well as the respiratory pathogens Strep. pyogenes, Staph. aureus and Moraxella. A 2014 study looked at the effect of adding either oil of the oregano plant (Origanum vulgare), carvacrol, thymol or a control to an antibiotic regimen against the organism Staph. aureus. The oregano oil and each of the phenols increased the inhibition of bacteria when added to the drug tetracycline, but none had any effect on the inhibition caused by the drugs erythromycin or norfloxacin. Also, oregano alone and carvacrol alone have shown activity against the norovirus, which causes gastrointestinal illnesses.

As for whether this anti-microbial effect translates to the world outside of a petri dish, only one good human study shows any efficacy. It looked at 14 patients who had non-pathogenic (not linked to illness) parasites in their stool. The participants were given 600 milligrams of oregano oil (Origanum vulgare) for six weeks. The study showed reduction or elimination of the parasites with the use of oregano oil. There was no placebo portion of the trial.

When it comes to cancer, Origanum vulgare has shown inhibition of cells in both breast and colon cancer. Another species, Origanum majorana, commonly known as sweet marjoram, stops the replication of liver cancer cells within the lab. A 2017 study in the European Journal of Nutrition looked at rats that were given medications to induce breast cancer. The 75 rats were separated into three groups: 25 were given 3 percent Origanum vulgare, 25 were given 0.3 percent and the last 25 were not given oregano. After 15 weeks of the study, the group given 0.3 percent oregano had a 44 percent reduction in the incidence of breast tumors. However, the rats given the 3 percent oregano had no reduction in the incidence of breast tumors. So maybe there is a Goldilocks zone for oregano. But again, human studies are nonexistent.

Some people report nausea and bloating with oregano oil, but overall, it appears safe. A 90-day study of oregano oil in rats found no adverse effects.

As for whether oregano oil has benefits, the answer is a solid maybe. No controlled human trials can even say whether it's effective against either infection or cancer. Some of the individual components such as carvacrol and thymol should be further studied in humans.

(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.)