Bacterial enteropathogens cause about 80% of cases. Viruses and protozoans account for most of the rest.The most common causative agent isolated in countries surveyed has been enterotoxigenic Escherichia coli (ETEC). Enteroaggregative E. coli is increasingly recognized. Shigella spp. and Salmonella spp. are other common bacterial pathogens. Campylobacter, Yersinia, Aeromonas, and Plesiomonas spp. are less frequently found. Mechanisms of action vary: some bacteria release toxins which bind to the intestinal wall and cause diarrhea; others damage the intestines themselves by their direct presence.Brachyspira pilosicoli pathogen also appears to be responsible for many chronic intermittent watery diarrhea and is only diagnosed through colonic biopsies and microscopic discovery of a false brush border  on H&E or Warthin silver stain: its brush-border is stronger and longer that Brachyspira aalborgis brush-border. It is unfortunately often not diagnosed as coproculture does not allow growth and 16S PCR panel primers do not match Brachyspira sequences.While viruses are associated with less than 20% of adult cases of travelers diarrhea, they may be responsible for nearly 70% of cases in infants and children. Diarrhea due to viral agents is unaffected by antibiotic therapy, but is usually self-limited. Protozoans such as Giardia lamblia, Cryptosporidium and Cyclospora cayetanensis can also cause diarrhea. Pathogens commonly implicated in travelers diarrhea appear in the table in this section.A subtype of travelers diarrhea afflicting hikers and campers, sometimes known as wilderness diarrhea, may have a somewhat different frequency of distribution of pathogens. Risk factors
The primary source of infection is ingestion of fecally contaminated food or water.
Folic acid supplements are also recommended for some cases of thalassemia. Evaluation and Diagnosis
In theory, the three most common microcytic anemias (iron deficiency anemia, anemia of chronic disease, and thalassemia) can be differentiated by their red blood cell (RBC) morphologies. Anemia of chronic disease shows unremarkable RBCs, iron deficiency shows anisocytosis, anisochromia and elliptocytosis, and thalassemias demonstrate target cells and coarse basophilic stippling. In practice, though elliptocytes and anisocytosis are often seen in thalassemia and target cells occasionally in iron deficiency. All three may show unremarkable RBC morphology. Basophilic stippling is one morphologic finding of thalassemia which does not appear in iron deficiency or anemia of chronic disease. The patient should be in an ethnically at-risk group and the diagnosis is not confirmed without a confirmatory method such as hemoglobin HPLC, H body staining, molecular testing or another reliable method. Coarse basophilic stippling occurs in other cases as seen in Table 1.As IDA and ACD can often be confused, it is important to evaluate their laboratory parameters. IDA is associated with low hemoglobin, ferritin, transferrin saturation, and MCV. It is also associated with a normal C-reactive protein and high transferrin. ACD is associated as well with low hemoglobin but ferritin may be normal-high, and transferrin saturation, transferrin, and MCV may be low-normal. An additional difference between IDA and ACD is that ACD is often associated with high C-reactive protein. See also
Hypochromic anemia

References
External links

Emedicine on chronic anemia