Although over 28 disease pathogens have been found in bed bugs, transmission of these pathogens to humans has never been documented and is considered highly unlikely. For this reason, they are not considered a serious disease threat. Their medical significance is mainly limited to the itching and inflammation associated with their bite. Not everyone reacts to bed bug bites in the same fashion. Some people have reactions that are delayed for several days or more while others do not react at all. Reactions to bites can also vary significantly between individuals from a mild itchy welt to a more severe rash like symptom. The most common reactions appear as a raised, reddened welt similar to a mosquito bite. Bites tend to be very itchy and often appear in rows of 3-4 welts or more. There are currently a couple of explanations for why bites often appear in rows. The first explanation is based on the sensitivity of bed bugs to motion. A single bug may withdraw its mouthparts while feeding in response to the slightest disturbance (i.e. person twitches during sleep). After removing their mouthparts, the bug will move a short distance and then begin feeding again, resulting in several bites in a row caused by a single bug. The second explanation involves numerous bugs that are lined up one next to the other (typically along a fold in a bed sheet) all feeding at the same time (similar to cattle at a trough). The important point is that the number of welts does not always correlate with the number of bugs that bit the individual. Thus, just a few bugs can be responsible for many welts in a single evening.
It is also very important to realize that bed bugs cannot be diagnosed by the bite alone. While a medical professional can examine the bites, they can only conclude that the bite symptoms are consistent with those produced by bed bugs. This is not a confirmation however it does provide the grounds for suspecting that bed bugs may be present and that a professional should be called in to perform an inspection for the presence of bed bugs in the structure where the bites occurred.