Dear Doctor: When our dad gets sick, he pretty much collapses into bed for a few days. My mom teases him and calls it the “man flu.” To us kids, it’s a family joke, but a friend insists man flu is real. Is she right?

Dear Reader: We’re talking about “man flu” because Dr. Kyle Sue, an assistant professor at Memorial University of Newfoundland in Canada, got tired of being labeled a drama queen when he was laid low by a respiratory infection. According to the definition -- and, yes, it’s common enough to have made it into both the Oxford and Cambridge dictionaries -- man flu is “an illness such as a cold that is not serious, but that the person who has it treats as more serious, usually when this person is a man.”

The takeaway is that when it comes to getting sick, men can be wimps. But as Sue points out, the assumption that a man with the flu is exaggerating his symptoms and discomfort can inadvertently lead to improper or insufficient medical care. To that end, Sue set out to study man flu. He sifted through various scientific databases using keywords that would cull research related to viral respiratory illnesses and their outcomes in both women and men.

What he found was that, perhaps due to certain physiological differences between the sexes, a man’s immune system appears to react more forcefully to the influenza virus than a woman’s. That may sound like a good thing, but the aches, pains, fever, chills and outpouring of mucus that typically accompany the flu are all courtesy of your immune system’s best efforts. A stronger immune response means worse symptoms.

The differences begin in the test tube. Nasal cells from both women and men were infected with the influenza virus. When the women’s cells were exposed to estradiol, a female hormone, the immune response was more moderate. When the men’s cells were exposed to the same amount of estradiol, the hormone had no effect on the level of the immune response, which was more robust. When it comes to the flu vaccine, the protective antibody response in women appears to be better than in men. One theory links this to testosterone, as men with higher levels of the hormone produced fewer flu antibodies. So even despite a flu shot, a man may still get sick. Other studies that tracked flu-related hospitalizations and deaths found men represented in higher numbers than women. As to the evolutionary advantage to what Sue calls the “immunity gap,” he said more study is needed.

The fact is that in a number of diseases and conditions -- including heart disease, osteoarthritis, urinary tract health, stroke, migraine, alcoholism and mental health issues -- women and men are affected differently. As for Sue, even as he calls for more research into the subject, he closed his paper with his tongue firmly planted in his cheek:

“Perhaps,” he wrote, “now is the time for male-friendly spaces, equipped with enormous televisions and reclining chairs, to be set up where men can recover from the debilitating effects of man flu in safety and comfort.”

(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: 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.)