Ask the doctors: Influenza and colds most commonly transferred through saliva

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.