Currently, extensive research is being conducted to determine associations between gastrointestinal dysfunction and a variety of human disorders that, heretofore, have been of unknown etiology.  For example, an association between dysautonomic conditions and gastrointestinal dysfunction has been described in U.S. patent application Ser.  No.  09/929,592, filed on Aug. 14, 2001, entitled “Methods For Diagnosing and Treating Dysautonomia and Other Dysautonomic Conditions, which is commonly owned and fully incorporated herein by reference.  Further, a relationship between gastrointestinal conditions and PDDs such as Autism, ADD (Attention Deficit Disorder) and ADHD (Attention Deficit Hyperactivity Disorder) has been described in detail in U.S. patent application Ser.  No.  09/466,559, filed Dec. 17, 1999, entitled “Methods For Treating Pervasive Development Disorders,” and U.S. Ser.  No.  09/707,395, filed on Nov. 7, 2000, entitled “Methods For Treating Pervasive Development Disorders”, both of which are commonly owned and incorporated herein by reference. 
Based on these findings, it is thus desirable to continue research in finding biologic markers of gastrointestinal dysfunction that may aid in the diagnosis of certain diseases and disorders.  For example, the effect of various pathogens on the gastrointestinal tract, and the association of such pathogens to disorders such as PDD and dysautonomia, has heretofore not been researched.  Various microorganisms that are of interest will now be discussed. 
Helicobacter pylori (H. pylori) is generally associated with chronic gastritis and peptic ulcer in children and adults.  The prevalence of H. pylori is highest in developing countries and lowest in developed countries.  Ethnicity, socioeconomic status, household crowding, and other conditions contribute to the formation of H. pylori infection.  Infection is rarely symptomatic in children, and duodenal ulcers are generally not seen in children less than 10 years of age.  Various diseases that are caused, or believed to be caused by H. pylori infection are known.  For instance, it has been postulated that H. pylori plays a role in auto-immune athero-sclerosis. 
Esophageal reflux disease (GORD) has further been postulated to be caused by H. pylori in a mechanism whereby somatostatin induces the hypothalamus to decrease the release of growth hormone from the pituitary affecting the adrenal control of cortisol.  The change in cortisol ultimately affects the gastrin release mechanism causing an increase in acid. 
Cryptosporidium parvum can be associated with infections of the gastrointestinal tract in children and in immunocompromised populations.  It is generally thought to account for up to 20% of all cases of diarrhea in developing countries and potentially life threatening in children with AIDS due to the induction of severe malnutrition.  These infections are generally asymptomatic and occur in tandem with other infections such as one with Giardia.  
In 1993, a large outbreak of Cryptosporidium parvum occurred in Milwaukee Wis. in which 400,000 people were affected.  It has a seasonal effect of being more prevalent in the late summer in children under the age of 15 years. 
Giardia lamblia is a common cause of diarrhea in humans and other mammals throughout the world.  In its most severe form, it has been found to cause infectious lymphocytosis.  Although rare, infection with Giardia can be protracted and debilitating.  Giardia lamblia is a flagellate that encysts, and generally does not cause symptomotology.  However, when found in the trophozoite form, severe diarrhea can result.  Symptoms can include diarrhea, vomiting, fatigue, and growth retardation in children.  Malabsorption results from infection with the trophzoite form, and potential blockage of the microvilli of the intestines occurs.  There may be an interaction between decreased levels of IgA in the gastrointestinal system and giardiasis. 
Clostridium infections of the gastrointestinal tract are of the perfringes, botulinum and difficele varieties.  Perfringens food poisoning is the term used to describe the common foodborne illness caused by C. perfringens.  A more serious but rare illness is also caused by ingesting food contaminated with Type C strains.  The latter illness is known as enteritis necroticans.  The common form of perfringens poisoning is characterized by intense abdominal cramps and diarrhea which begin 8-22 hours after consumption of foods containing large numbers of those C. perfringens bacteria capable of producing the food poisoning toxin.  The illness is usually over within 24 hours but less severe symptoms may persist in some individuals for 1 or 2 weeks.  A few deaths have been reported as a result of dehydration and other complications.  Necrotic enteritis caused by C. perfringens is often fatal.  This disease also begins as a result of ingesting large numbers of the causative bacteria in contaminated foods.  This disease is a food infection; only one episode has ever implied the possibility of intoxication (i.e., disease from preformed toxin). 
Clostridium difficile is an infection generally caused by changes in the intestinal mucosa.  Those changes are caused by an overuse of antibiotics creating an intestinal environment favorable to the infiltration with Clostridium difficile.  Infection with C. difficile is generally debilitating and C. difficile is a gram-positive, spore forming, anaerobic bacillus which can produce toxin-mediated diarrhea or pseudomembranous colitis.  It has been isolated from soil, sand, hay, and animal dung.  C. difficile colonization of the colon occurs in 2%-3% of healthy adults.  Following exposure to antibacterial agents, the rate of asymptomatic colonization in adults averages between 5% to 15%, but rates as high as 46% have been reported.  Carriage rates of up to 70% have been reported in children below the age of one year, but by two years of age the “normal” colonic flora is established and the frequency of colonization decreases to that of healthy adults.  Of interest is that healthy children less than one year of age are the only population in which C. difficile toxins are frequently detected in the stool in the absence of clinical symptoms.  One suggestion advanced to explain this observation is that the infant's gut cannot respond to the toxin. 
Clostridium botulinum is an anaerobic, spore-forming rod that produces a potent neurotoxin.  The spores are heat-resistant and can survive in foods that are incorrectly or minimally processed.  Seven types (A, B, C, D, E, F and G) of botulism are recognized, based on the antigenic specificity of the toxin produced by each strain.  Types A, B, E and F cause human botulism.  Types C and D cause most cases of botulism in animals.  Animals most commonly affected are wild fowl and poultry, cattle, horses and some species of fish.  Although type G has been isolated from soil in Argentina, no outbreaks involving it have been recognized.  Foodborne botulism (as distinct from wound botulism and infant botulism) is a severe type of food poisoning caused by the ingestion of foods containing the potent neurotoxin formed during growth of the organism.  The toxin is heat labile and can be destroyed if heated at 80° C. for 10 minutes or longer.  The incidence of the disease is low, but the disease is of considerable concern because of its high mortality rate if not treated immediately and properly.  Most of the 10 to 30 outbreaks that are reported annually in the United States are associated with inadequately processed, home-canned foods, but occasionally commercially produced foods have been involved in outbreaks.  Sausages, meat products, canned vegetables and seafood products have been the most frequent vehicles for human botulism. 
The life cycle of Entamoeba histolytica involves trophozoites (the feeding stage of the parasite) that live in the host's large intestine and cysts that are passed in the host's feces.  Humans are infected by ingesting cysts, most often via food or water contaminated with human fecal material.  The trophozoites can destroy the tissues that line the host's large intestine, so of the amoebae infecting the human gastrointestinal tract, E. histolytica is potentially the most pathogenic.  In most infected humans the symptoms of “amoebiasis” (or “amebiasis”) are intermittent and mild (various gastrointestinal upsets, including colitis and diarrhea).  In more severe cases the gastrointestinal tract hemorrhages, resulting in dysentery.  In some cases the trophozoites will enter the circulatory system and infect other organs, most often the liver (hepatic amoebiasis), or they may penetrate the gastrointestinal tract resulting in acute peritonitis; such cases are often fatal.  As with most of the amoebae, infections of E. histolytica are often diagnosed by demonstrating cysts or trophozoites in a stool sample.  Infections that sometimes last for years may be accompanied by no symptoms, vague gastrointestinal distress, and/or dysentery (with blood and mucus).  Most infections occur in the digestive tract but other tissues may be invaded.  Complications include ulcerative and abscess pain and, rarely, intestinal blockage.  Onset time is highly variable.  It is theorized that the absence of symptoms or their intensity varies with such factors as strain of amoeba, immune health of the host, and associated bacteria and, perhaps, viruses.  The amoeba's enzymes help it to penetrate and digest human tissues; it secretes toxic substances. 
No extensive research is known to have been conducted heretofore to determine correlations and associations regarding the presence of pathogens in the gastrointestinal tract of individuals in, e.g., PDD, Parkinson's and Dysautonmia populations.  Based on the findings described herein in accordance with the present invention, correlations and associations are found to exist between various disorders such as Autism, Parkinson's, ADD, ADHD and Dysautonomia, for example, and the presence of pathogens in an individual's digestive tract.