Dear Doctor: How contagious is spit? I read that an Ohio man with hepatitis C was sentenced to 18 months in prison for spitting at police officers and paramedics.

Dear Reader: You’re referring to an incident in Cleveland last January, when several police officers came to the aid of a man who was passed out on the sidewalk in the middle of the night. As the officers were helping to load him into an ambulance, he fought them and tried to get away. During the struggle, he spit at the people around him. According to police reports, the man hit one of the officers in the eyes, nose and mouth with his saliva, which was also mixed with his blood. The hospital later informed the officers that the man had hepatitis C.

Although the man was spitting, it wasn’t the saliva that posed the threat. Rather, it was the blood mixed in with the saliva that was potentially dangerous. Hepatitis C is transmitted when blood from a person who is infected with the virus enters the blood of someone who is not infected. Although the likelihood of transmitting the virus via the bloody spit was low, the affected police officers underwent subsequent testing and got clean bills of health. Ohio is among many states that have made it a felony to willfully expose someone to HIV, tuberculosis and viral hepatitis. It’s based on this law that the man was charged, tried and sentenced.

When we’re talking about spit, we really mean saliva. It’s produced by the salivary glands throughout the day and, to a lesser extent, during the night. Although it’s 98 percent water, it’s the makeup of that remaining 2 percent -- which includes mucus, electrolytes, a range of enzymes and antibacterial compounds -- that makes saliva kind of amazing. The digestive process starts in the mouth, where saliva moistens food and makes it easier to swallow, and where the enzyme amylase begins the breakdown of certain carbohydrates. The constant flow of saliva flushes away debris in the mouth, and another enzyme, lysozyme, battles bacteria. When we sleep, saliva production slows down. That allows an overnight buildup of bacteria, which is why we wake up with morning breath.

As for diseases that can be transmitted through saliva, influenza and the common cold are probably the most common. Direct contact with saliva can also expose you to the enteroviruses that cause a certain type of bacterial meningitis, the Epstein-Barr virus, oral herpes and gingivitis. Sharing a glass or eating utensils, using someone else’s toothbrush and kissing are all ways that you can inadvertently come into contact with someone else’s saliva. It’s important to note that exposure to infectious agents does not automatically translate into developing the disease.

Perhaps most interesting is the ongoing research into the idea of saliva as a diagnostic tool. Scientists suspect that within that non-water 2 percent of saliva are proteins, antibodies and nucleic acids that may be biomarkers of both localized and systemic disease. The hope is for a breakthrough that can lead to the use of saliva both as a diagnostic tool for disease states and as a way to monitor general health.

(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: Our 92-year-old mother, who’s still sharp as a tack, was perfectly fine one moment and then suddenly became weak and extremely disoriented. It was like she had dementia. We expected to hear that she had suffered a stroke, but hospital tests showed she had a UTI. Why would that affect her mind? And why didn’t she ever have any other symptoms?

Dear Reader: A urinary tract infection, or UTI, often presents differently in the elderly than in younger individuals. The typical symptoms we’re familiar with -- which include a burning sensation during urination; scant urinary output despite a frequent urge to go; urine that is cloudy, dark or that smells strange; and pressure or pain in the abdomen -- frequently do not show up. Instead, the first sign that an elderly person has contracted a UTI can often be what you have described -- a sudden change to their well-being and demeanor. These infections can lead to serious problems, such as kidney damage or even sepsis, so “silent” UTIs present a real health threat to the elderly.

A UTI occurs when any part of the urinary system, which includes the urethra, bladder, ureters and kidneys, becomes infected with bacteria. The urethra is the duct through which urine flows from the bladder and out of the body. The ureters are the ducts that convey urine from the kidneys to the bladder. Because the urethra is shorter in women than in men, and because it is located so close to the rectum, a potential source of bacteria, UTIs tend to be more common in women than in men.

It’s possible that the reason older adults often fail to produce noticeable symptoms is that the physical changes that signal a UTI are the result of the immune system fighting off the infection. As we age, our immune systems tend to slow down, so an infection can be more advanced by the time any symptoms show up.

The first symptom that some older adults will notice is lower back pain, which happens when the infection has reached the kidneys. In post-menopausal women, changes to the urinary tract can make them more vulnerable to infection. In men, prostate issues can result in incomplete emptying of the bladder, which leaves them vulnerable to infection. As for why UTIs are associated with altered mental status in the elderly, the reasons aren’t completely clear. One theory is that the surge in inflammation, which can affect the neurotransmitters that help nerve cells to communicate, interferes with normal brain function.

A urinalysis can reveal the presence of certain compounds in the urine that suggest a UTI. A urine culture will pinpoint the specific bacterial culprit. The good news is that UTIs respond well to antibiotics. As with all antibiotic therapies, it’s vital to take the entire course that has been prescribed. In patients whose UTI had no symptoms, we also think it’s a good idea to consider a follow-up urine culture a few days after the antibiotic therapy is complete. This will confirm that the UTI has cleared up completely.

(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.)

Hello again, dear readers! It's been a busy month for letters, so we'll get right to it.

-- Regarding a column about post-operative cognitive dysfunction (POCD), in which elderly patients experience mental disruptions following surgery, we heard from an anesthesiologist in Florida. In our column, we explored the link the condition has to general anesthesia. However, he points out that the stress of surgery in and of itself can lead to POCD, and that a more accurate definition is an "impairment to the mental functions of an individual following surgery."

His concern is that isolating general anesthesia as the cause "will create unnecessary fear for elderly patients scheduled for general anesthesia, as there are no definitive studies showing that one form of anesthesia is better than another in preventing POCD. Patients may request a less-than-optimal form of anesthesia in the misguided belief that it would prevent POCD."

-- We recently wrote about a fascinating study in which researchers found that a wound sustained during the day heals twice as fast as one sustained at night. A reader from Louisville, Ohio, wondered whether this applies to the operating room as well.

"What about surgery, since that is a type of wound, and since many doctors like to do surgery early in the morning, is there any evidence about faster healing for surgery done at any special time of day?"

The answer is yes, the time at which surgical cuts are made affects their healing rate as well. The study tied the speed of wound healing to the body's circadian clock, the rhythms of which are keyed to daylight and darkness. The incisions from an emergency surgery performed at night healed more slowly than similar daytime incisions. Although the study didn't go into differences in healing rates between early-morning wounds and afternoon or early-evening wounds, we'd love to see that data.

-- Regarding nighttime leg cramps, many of you offered home remedies.

A reader in Pennsylvania wrote that "when attacked by leg cramps in the middle of the night, I manage to make it into the kitchen and put a rice bag in the microwave for a minute or so. The heat from that, or even a hand towel run under very hot water and wrung out, is very effective when applied to the cramp."

A reader from Simi Valley, California, says that standing tall and then slowly bending forward, aiming for the floor ("if your knees hurt, as mine now do at 74, I bend them a bit") delivers a thigh and calf stretch that helps banish cramps.

One more, from a reader who drinks "1/2 to 1 teaspoon of baking soda in a glass of water (and no, it is not the water by itself that does it, I've tried). The cramp will be gone within a minute or two. Gone are even the agonizing cramps in my groin that drove me crazy. I keep baking soda by my sink in my bathroom so it's handy whenever I need relief."

Thank you, as always, for your thoughts, corrections, thanks and encouragement. It's a pleasure to hear from you.

(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.)