Dear Doctor: We live in Orlando, and last year a teenager here was infected with that brain-eating amoeba. Now we're reading that it's in the drinking water in Louisiana. How common is it? Should we be worried about an epidemic?

Dear Reader: There's nothing quite like the words "brain-eating amoeba" to get the news cycle humming. And the reassurance we're about to give you -- it is extremely, exceedingly rare -- is not necessarily the most attention-grabbing. But that's where we're going to begin.

Between 2007 and 2016, there have been just 40 cases of the so-called brain-eating amoeba reported in all of the United States, according to the Centers for Disease Control and Prevention. To put that into even clearer perspective, that's 40 cases in 10 years among 324 million people.

The microscopic creature that's been making headlines is called Naegleria fowleri. Trace amounts of it were discovered in two community water systems in southern Louisiana during routine testing last June. Customers of the affected water facilities were promptly alerted by the Louisiana Department of Health, and disinfection procedures were implemented.

So what is it?

Naegleria fowleri is a single-celled organism found throughout the world in warm freshwater, like lakes, streams, rivers, ponds and hot springs. It enters the body through the nose, typically when people accidentally inhale water while swimming or diving. The amoeba then travels through the nasal passages and enters the brain via the olfactory nerve. Once there, it begins to destroy brain tissues.

You can't become infected by drinking contaminated water, or by swimming in water that has been adequately chlorinated. There have been no known cases of transmission through water vapor, as during a shower or through a humidifier.

The majority of infections reported since 1962 have been in the southern U.S., with half of those in Florida and Texas. But infections have occurred as far north as Minnesota and as far west as Nevada and California. The specific disease the organism causes is called primary amebic meningoencephalitis, or PAM. It's diagnosed using specific laboratory tests that, because the disease is so rare, are not widely available.

Symptoms begin one to nine days after infection, and are divided into two stages. They're similar to those of bacterial meningitis, which adds a level of difficulty to an accurate diagnosis.

The first stage of the disease is marked by a severe headache in the front of the head, often with fever, nausea and vomiting. This is followed by stiffness in the neck, altered mental state, seizures and coma.

Although in most cases the disease is fatal, the Orlando teenager you're referring to survived. It is believed that a swift diagnosis -- the infection was identified within hours of the onset of symptoms -- was key to his beating the odds. So was aggressive treatment, which included an investigational drug, and cooling his body to well below normal body temperature, a process known as therapeutic hypothermia.

Unlike other survivors, who had permanent neurological damage, the Orlando teen recovered fully and is back in school. The hope is that early diagnosis and novel therapeutics may lead to higher survival rates in the future.

(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 read that you can use your own stem cells to rejuvenate worn-out knees. Does this really work?

Dear Reader: "Worn out" is a good way to term what happens to the knee joint with prolonged use. Let's look at how this happens, starting with cartilage.

The lower portion of the knee joint (at the tibia) contains shock absorbers -- called menisci -- made of cartilage. You have one on the inner portion and another on the outer portion of each knee. The upper portion of the knee joint (at the femur) is lined with cartilage as well. All of this cartilage helps protect the bones at the joint -- but it doesn't heal or regenerate well due to limited blood supply. When severe, worn cartilage leads to arthritis of the knee. In knee X-rays of people over the age of 60, 37 percent have shown evidence of arthritis of the knees.

The intriguing thing about stem cells is that they have the ability to become any type of cell that the body needs. The cells used for stem cell injections in the knees are called mesenchymal stem cells, and they can differentiate into bone, fat or cartilage cells. These stem cells can come from the fat cells of your body, from your bone marrow or from the inner lining of your knee joint; they're then replicated in the laboratory and injected into the knee joint.

Here's what the research shows so far ...

In a 2013 study, 32 patients with meniscal tears of the knee were injected with a combination of stem cells, platelet-rich plasma and hyaluronic acid. The study reported improved symptoms and even MRI evidence of meniscal cartilage regeneration.

In a 2014 study, 55 patients who had surgery for meniscal tears of the knees were separated into three groups, with two of the groups receiving stem cell injections. Researchers found that, after six weeks, pain had decreased substantially in the two groups that received stem cell injections and that the decrease was even greater at one and two years after the injection.

In a 2017 study in the British Journal of Sports Medicine, researchers analyzed six studies that used stem cells for osteoarthritis of the knees. In five of the studies, stem cells were given after surgery to the knee; in the other study, stem cells from a donor were administered without surgery. All the studies showed reduced pain and improved knee function. Further, in three of the four trials, MRIs corroborated the cartilage improvements. However, the authors noted, five of the six studies were of such poor methodology that an overall conclusion about the stem cells' effectiveness could not be made.

In all these studies, the most common side effect was knee swelling and stiffness, which improved over time.

There may be benefit to stem cell injections for cartilage loss of the knees, but more data are needed, especially in those who aren't having surgery of the knee. I'd also like to see more data on this type of therapy as a preventive measure for younger patients -- before their knees are worn out.

(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: Is there anything I can do to keep my doctor from interrupting me? He's a really nice man, and I know he's busy, but I never get to share all of my concerns or have my questions answered before the visit is over.

Dear Reader: You've brought up an issue that's getting a lot more attention than it once did, and one that doctors in all specialties are actively working to address. We do have some specific strategies, but first, allow us to nerd out a bit.

A study on this subject with a statistic that often gets cited -- that on average, a patient speaks for about 17 seconds before the physician cuts in -- was conducted all the way back in 1984. Subsequent studies, which used larger sample sizes, highlighted the same challenge. These days, the amount of time a patient gets to speak uninterrupted has edged up about 50 percent. But considering that's now in the neighborhood of 25 seconds, it doesn't seem like much of an improvement.

So what can you do?

Begin your appointment with a mission statement. Politely tell your doctor that, before he or she responds, you would like the chance to lay out all your questions and concerns. This may sound like you're asking permission for an interminable monologue. However, in studies where patients were allowed to speak without interruption, it took them between 90 seconds and two minutes to present their information.

So you've said your piece. Now, it's your turn to help things move smoothly.

Begin by listing the things you want the doctor to address. Perhaps you have a specific medical issue, and you also want general advice about another topic or two. Make that clear. This will let your doctor mentally prepare for how best to spend the remaining time in your appointment.

If you do have a specific medical issue, be prepared with a concise and fact-filled narrative. Tell him or her when the symptoms began, how and when they changed or escalated, and what they feel like. A burning sensation, a stabbing pain, an ache that occurs when you move a certain way -- all is useful diagnostic information.

When you're finished speaking and are ready to listen, let your doctor know. And when he or she begins to answer, pay attention. Take notes. If something that is said needs follow-up questions, make a note of it. As the visit ends, use your notes to quickly summarize the information and instructions. This way, you both know you're on the same page.

Sometimes you do wind up with follow-up questions once the appointment ends. Here at UCLA we have an electronic communications portal that our patients can use to reach us. Perhaps your medical provider has something similar. Ask for a few minutes with a nurse or physician's assistant. And don't be afraid to make another appointment if you feel that's what you need.

Life in a doctor's office moves quickly these days. We understand that speaking up can be uncomfortable for you (and perhaps even for your doctor). But when you do, we believe both of you will come away with a greater sense of satisfaction.

(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.)