2.4 Diagnosis confirmation

2.4.1 Clinical examination

The doctor or nurse of the investigation team should examine suspect cases and verify that the clinical signs are compatible with cholera: acute watery diarrhea (3 or more liquid stools in 24 hours) with no visible blood in the stool, with or without vomiting and/or dehydration.
Laboratory investigations are to be performed in those presenting with compatible clinical signs.

2.4.2 Laboratory investigations

At this stage, laboratory investigations are carried out to confirm the causative agent and determine the sensitivity of the strain to antibiotics.

Rapid diagnostic tests (RDTs)
RDTs are intended to screen suspect cases to determine if Vibrio cholerae O1 or O139 might be the causal agent. However, only culture can confirm the etiological diagnosis.
There is no evidence-based recommendation for the number of RDT to perform for optimal detection of cholera transmission. In addition, none of the currently available RDTs is pre-qualified by the WHO. As long as there are no pre-qualified RDTs, this guide recommends collecting stool sample for microbiological diagnosis without prior RDT screening.

Culture of stool specimens
– Stool specimens (Appendix 1) are sent to a properly equipped microbiology laboratory to:
• Confirm cholera;
• Identify the strain (serogroup/biotype/serotype);
• Assess antibiotic sensitivity.
– 4 to 10 stool samples should be sent to the reference laboratory.
– Check with the laboratory for preferred transport media (filter paper or Cary-Blair).

Notes:
– Management of cases of acute watery diarrhoea should not wait for microbiologic confirmation of cholera.
– During an outbreak, cultures and antibiotic susceptibility testing on 3 to 5 patients should be repeated monthly to confirm the on-going presence of Vibrio cholerae and to determine any changes in antibiotic susceptibility patterns. When the number of cases decreases progressively and the end of the outbreak seems to be imminent, these tests should be performed each week.