Bacteria and viruses are present on virtually every surface we come in contact with in our day to day life, but the reality is that only a small proportion of these microbes are pathogenic (have the potential to cause disease). Most reputable spas and massage therapy establishments clean the beds well between clients. If you are concerned, you should ask the establishment you are considering going to what sanitation procedures they have in place. In general, the best and easiest way to sanitize a surface is to use either alcohol or bleach left in place until it air dries.
An increasingly common and concerning pathogen spread by surfaces such as those in gym locker rooms or health spas is community acquired methacillin resistant staphlococcus aureus (MRSA). This a bacterial pathogen that commonly causes skin infections such as boils, abscesses, and cellulitis. Some of these infections can be severe, especially in debilitated populations such as the elderly, people with abnormal immune function, or those suffering from certain other debilitating diseases. That said, with appropriate sanitization procedures in place, the likelihood of contracting any illness
from a massage table wound be very unlikely, although not impossible.
If you want to get an accurate picture of your likelihood of getting ill from lying on a massage table, I would do these things: Contact the establishment you are thinking of going to and discuss their sanitization practices, make an appointment to see a primary care physician
who can evaluate your susceptibility to infection and give you a realistic ideal of what community acquired pathogens are prevalent in your area, and take a shower and clean yourself with antibacterial soap after the experience.