Focal infection: new age or ancient history?

A focus of infection is a confined area that: (1) contains pathogenic microorganisms, (2) can occur anywhere in the body and (3) usually causes no clinical manifestations (1). A focal infection is a localized or generalized infection caused by the dissemination of microorganisms or toxic products from a focus of infection (1). These concepts have led to the Focal Theory of Infection (or Theory of Focal Infection) that postulates a myriad of diseases caused by microorganisms (bacteria, fungi, viruses) that arise endogenously from a focus of infection. Some have expanded this to include the environment via the concept of antigenic (molecular) mimicry or even to the extent that all diseases are caused by microbes (2, 3). Foci of infection have historically been postulated to arise from the tonsils, adenoids, sinuses and oral cavity with less common foci from the prostate, appendix, gall bladder and kidney (4, 5). Oral foci have traditionally been ascribed to pyorrhea alveolaris (periodontitis), alveolar abscesses and cellulitis, pulpless teeth, apical periodontitis, general oral sepsis and endodontically treated teeth with viridans group streptococci (VGS) being the principal metastatic microbial culprits (1, 4, 5). Focal infections attributed to foci of infection have included arthritis, neuritis, myalgias, nephritis, osteomyelitis, endocarditis, brain abscesses, prosthetic joint infections, skin abscesses, pneumonia, asthma, anemia, indigestion, gastritis, pancreatitis, colitis, diabetes, emphysema, goiter, thyroiditis, Hodgkin’s disease, fever of unknown origin, stupidity and ‘nervous diseases of all kinds’ (1, 6–8). Currently, diseases postulated to be caused by microorganisms include cancer (9), sarcoidosis, multiple sclerosis, amyotrophic lateral sclerosis, autism, Guillain–Barré syndrome, pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS), Tourette’s syndrome, myasthenia gravis, polycystic kidney disease, obesity, Alzheimer’s disease, diabetes mellitus and, of particular interest to dentistry, cardiovascular disease (4, 10). Many of these are proposed to affect the host by antigenic mimicry: microbial antigens similar to host antigens that induce an immune response that damages host tissue (11). The classic pathway of focal infection is by direct spread via blood or lymphatic metastasis of the infecting microorganism, its toxic products or tissue-damaging immunologic reactions to the microorganism. Several characteristics consistently appear throughout the long history of focal infection: (1) theories of disease espoused by authoritative (some might say autocratic) individuals with little or no science to support their theses (doctrine without data), (2) consistent application of focal infection to diseases for which medicine has no good concepts of etiology and/ or treatment, (3) consistent and pervasive extrapolation beyond the data and (4) a common disregard for the accepted methodology of science (i.e. controlled studies). Often, the ‘disregard syndrome’ is apparent: the unintentional failure to cite previous scientific works, scorn for previous sound published data that is not considered ‘cutting edge’, apparently intentional disregard for already published data that does not conform or even contradicts the position espoused by the investigator or an unintentional lack of regard for relevant literature due to ignorance of the field being investigated (12). ‘Reverse Investigation’ is not uncommon: start with the conclusion and then gather only the facts that support it. The tendency to programmed conferences is common: only those who are of the samemind are invited and commonly leads to what Jane’s Defense Weekly terms ‘incestuous amplification’: a condition in warfare where one only listens