Long-term carriage is possible but not common (most significant in practice in salmonellosis)
In 1-3% of patients with acute gastroenteritis abdominal symptoms become prolonged.
EPEC and EAEC (enteropathogenic and enteroaggregative E. coli) may sometimes be associated with prolonged symptoms.
Viruses
Cause acute disease; prolonged symptoms are rare.
Asymptomatic excretion of viruses may continue for several weeks or even several months after the acute infection (particularly in those with immunodeficiencies).
Intestinal protozoans
The longer the symptoms continue, the more probably they are caused by protozoans.
In the beginning, the infection is often either asymptomatic or produces few symptoms.
Entamoeba histolyticaAmoebiasis usually causes more severe diarrhoea than the above and symptoms often include blood in stools and sometimes also fever.
The infection is often either asymptomatic or produces few symptoms.
Strongyloides stercoralisStrongyloidiasis (the most common cause of symptomatic worm infections in travellers), Ascaris lumbricoides, or roundworm Ascariasis, hookworms Hookworm Disease and Trichuris trichiura Trichuriasis cause the most symptoms. Toxocara, a dog and cat parasite endemic worldwide, can also cause prolonged abdominal complaints.
Other worms cause symptoms only at a high worm load; in practice these are seen only in people who have lived very long in endemic areas.
Antibiotic-associated diarrhoea (symptoms related to the use of antimicrobial drugs)
Occurs in 5-25% of patients on antimicrobial drugs.
In some, symptoms occur already a few hours, in others as long as several weeks after the initiation of the medication.
Antimicrobial drugs destroy the patient's own intestinal microbes, broad-spectrum antimicrobials more so than narrow-spectrum antimicrobials.
Microbial imbalance may appear as overgrowth of Clostridioides difficile bacteria, for example.
Life-threatening pseudomembranous colitis is the most severe form of the disease.
Non-infectious abdominal complaints triggered by microbes
Microbes may sometimes trigger a non-infectious disease even if the causative agent can no longer be shown after prolonged symptoms. Acute gastroenteritis, for example, may trigger a chronic inflammatory bowel disease, such as Crohn's disease Crohn's Disease or ulcerative colitis Ulcerative Colitis.
Symptoms may persist for as long as several months.
Secondary malabsorption in some protozoal diseases, such as giardiasis
May be due to damaged intestinal villi.
The most common form of secondary malabsorption is secondary lactose intolerance, a state of disease sometimes resembling coeliac disease.
The symptoms will subside as the intestinal villi recover.
Abdominal complaints that last for less than one week after travelling do not usually require more detailed examination.
If symptoms continue (for more than 2 weeks), infectious causes should be sought, and also noninfectious causes, as necessary.
Bacterial causes
If aetiological investigations are needed, the basic study is the combination of nucleic acid detection for and bacterial culture of faecal pathogens. Nucleic acid detection identifies the bacteria listed below.
Salmonella
Shigella
Yersinia
Campylobacter
Escherichia coli strains causing diarrhoea
Enteroaggregative (EAEC)
Enteropathogenic (EPEC)
Enterotoxigenic (ETEC)
Enteroinvasive (EIEC)
Enterohemorrhagic (EHEC)
For any sample for which the nucleic acid detection method gives a positive result for Salmonella, Shigella, Yersinia, Campylobacter or EHEC, a culture and, if needed, sensitivity testing, are done without separate request. Laboratory-specific differences may exist.
Serological methods (Salmonella, Campylobacter and Yersinia antibodies) are used
when the symptoms have continued for more than 2 weeks and the aetiology is still not known
when reactive arthritis is suspected
when investigating prolonged unclear episodes of fever
when general symptoms occur.
In patients who have taken antimicrobials, nucleic acid detection test for Clostridium difficile is also performed. Nucleic acid detection is a sensitive test and should not be used in persons with no symptoms. In children below 2 years of age, C. difficile is a part of normal intestinal flora.
Biphasic diagnosis of parasitic infections
Protozoans are common parasites.
As an example, in Finnish patient samples (population 5.5 million), protozoans are the most common parasites. Thousands of cases of Dientamoeba are found annually, while during the same period, 150-300 cases of Giardia and 400-600 cases of Cryptosporidium are found. In recent years, the number of cases ofCryptosporidium andDientamoeba detected has increased substantially compared to the early 2010s, largely due to nucleic acid amplification tests.
Intestinal worms are clearly more rare findings than protozoans (country-specific differences may apply). In biphasic diagnosis, protozoans are first looked for and intestinal worms only in the second phase.
Phase one
Detection of the nucleic acids of intestinal protozoans in faeces is excellent for the investigation of prolonged abdominal complaints. The test can also detect Dientamoeba and Cryptosporidium. Check the description of the test performed by the local laboratory and whether detection of specific pathogens need to be separated asked for in the laboratory request.
If no pathogen is found in phase 1 test, move on to phase 2.
Other investigations depending on the clinical picture (basic investigations include e.g. CRP, basic blood count with platelets, sodium, potassium, creatinine and ALT).
Phase two
Examination for faecal parasites (microscopy for protozoan cysts, as well as helminth eggs and larvae) from three different stool samples to exclude intestinal worms
Formalin samples should be collected on 3 different days, preferably every couple of days
The examination does not detect Dientamoeba and Cryptosporidium and neither does it differentiate between the pathogenic Entamoeba histolytica and the apathogenic E. dispar.
Suitable for the examination of intestinal worms (helminth eggs)
The nucleic acid detection test for intestinal protozoans should be performed again using 1-2 samples taken on different days
Blood eosinophil count or automated differential plasma leucocyte count
Eosinophilia may be associated with a worm infection (e.g. Strongyloides stercoralis Strongyloidiasis).
If the patient has clear eosinophilia without other diseases explaining it (e.g. asthma or symptomatic allergy), ask a physician specialized in infectious diseases or gastroenterology for assessment.
If the examinations for faecal parasites (microscopy) give negative results and the patient has no eosinophilia, worm infections are unlikely (but pinworm is still possible).
Other tests include e.g. HIV antigen and antibody, TSH, CRP, ESR, sodium, potassium, creatinine, ALT, GT, blood lactose intolerance (DNA test), tissue transglutaminase antibodies, faecal calproctetin.
A serum worm antibody test is in certain cases requested after consulting a specialist in infectious diseases. It is used to seek antibodies to seven worms often found in patients with eosinophilia (e.g. Strongyloides, Toxocara and Schistosoma). Toxocara cannot be detected in faecal samples. It is a canine and feline parasite that in humans remains migrating in the larval stage in the intestine (visceral larva migrans) and may cause abdominal complaints continuing several months without diarrhoea.
Treatment
If a specific causative agent is found, proceed accordingly.
Metronidazole - first-line choice in outpatient care (moderately effective)
Secnidazole and tinidazole - possibly under special license (less effective than paromomycin)
Paromomycin - possibly under special license (highly effective). The drug is relatively expensive, so some patients are still treated with metronidazole and, if necessary, referred to specialized care if treatment fails.
Quinacrine (mepacrine) - possibly under special license (for treatment-resistant giardiasis)
Blastocystis hominis
Common faecal finding
Usually considered apathogenic, medication not necessary
Shows previous contact with faecally contaminated water or food; more samples need to be collected to find the pathogenic parasite.
If the organism is detected repeatedly in large amounts and without other explanation for the abdominal complaints, treatment with metronidazole or paromomycin, for example, can be considered.A therapeutic trial may in some cases reduce symptoms because the drug may be effective against pathogenic protozoans not detected in tests or otherwise changes the microbial balance in the intestine.
Even if the symptoms of protozoan disease are alleviated or cease during treatment, they may recur after the end of the treatment. In that case new samples should be collected. The reason may be:
drug resistance
Giardia may be resistant to metronidazole but this is not common.
Other intestinal parasites are hardly resistant.
re-infestation acquired at home or fromother close contacts (e.g. Dientamoeba)
relapse caused by surviving parasites sensitive to the drug
In giardiasis, a 5-10% risk
In Entamoeba histolytica infections relapses are common unless specially licensed drugs effective against cysts are used
insufficient patient compliance.
Empirical pharmacotherapy
As suggested by a physician specialized in infectious diseases if there is a strong suspicion of a parasite infection
Symptoms of malabsorption secondary to damage to intestinal villi associated with parasite infections (particularly giardiasis) can be alleviated by a lactose-free diet rich in fibre, sometimes also by a gluten-free (i.e. coeliac) diet.
References
Pietilä JP, Meri T, Siikamäki H, et al. Dientamoeba fragilis - the most common intestinal protozoan in the Helsinki Metropolitan Area, Finland, 2007 to 2017. Euro Surveill 2019;24(29):. [PubMed]
van Gestel RS, Kusters JG, Monkelbaan JF. A clinical guideline on Dientamoeba fragilis infections. Parasitology 2019;146(9):1131-1139. [PubMed]
van Lieshout L, Roestenberg M. Clinical consequences of new diagnostic tools for intestinal parasites. Clin Microbiol Infect 2015;21(6):520-8. [PubMed]