The cornerstone of confirming a cholera diagnosis is laboratory testing. This primarily involves isolating Vibrio cholerae from a patient’s stool sample, followed by serotyping to identify O1 and O139 strains. While traditional stool cultures remain vital, molecular methods like Polymerase Chain Reaction (PCR) are increasingly utilized due to their enhanced sensitivity and accuracy in Cholera Disease Diagnosis.
For suspected cholera cases, healthcare providers should request a stool culture on thiosulfate-citrate-bile salts-sucrose (TCBS) agar. This selective medium is the gold standard for isolating and identifying Vibrio cholerae. However, in cases of severe symptoms, prompt treatment should be initiated without waiting for culture confirmation.
Vibrio cholerae bacteria colonies thriving on Thiosulfate-Citrate-Bile Salts-Sucrose (TCBS) agar plate, a selective medium crucial for laboratory diagnosis of cholera.
To ensure sample integrity during transit to the lab, Cary Blair Transport Medium is the recommended method for stool specimen transport.
Rapid diagnostic test (RDT) kits for cholera are available commercially and are valuable tools during epidemic outbreaks for rapid preliminary identification. However, RDTs have limitations as they do not provide bacterial isolates needed for antimicrobial susceptibility testing and detailed subtyping. Therefore, RDTs are not recommended for routine cholera disease diagnosis.
Vibrio cholerae O1 and O139 Serogroups in Cholera Diagnosis
Vibrio cholerae serogroups O1 and O139 are significant in cholera disease diagnosis because they are known to produce a potent toxin that causes the severe diarrheal illness characteristic of cholera.
Only toxigenic strains belonging to serogroups O1 and O139 are responsible for widespread cholera epidemics and are mandatorily reported to the World Health Organization (WHO) as confirmed cholera cases.
Within Vibrio cholerae O1, two biotypes exist: Classical and El Tor. The El Tor biotype further encompasses serotypes Inaba, Ogawa, and the less common Hikojima. Clinically, infections from these serotypes are indistinguishable. Notably, infections with the El Tor biotype often present as asymptomatic or mild illness in a higher proportion of individuals.
Infections caused by the Classical biotype of Vibrio cholerae O1 are now infrequent, primarily confined to regions within Bangladesh and India.
It’s important to note that various other Vibrio cholerae serogroups, regardless of their cholera toxin gene presence, can induce cholera-like illnesses. Even non-toxigenic strains of O1 and O139 serogroups, along with serogroups like Vibrio cholerae O75 and O141, have been implicated in diarrheal illnesses linked to seafood consumption or exposure to contaminated water sources such as lakes and rivers.
Reporting Cholera Cases for Public Health Surveillance
Cholera is a nationally notifiable disease in many countries, including the United States, underscoring the importance of public health surveillance. For comprehensive cholera surveillance and control, it is imperative that all Vibrio cholerae isolates are forwarded to public health laboratories, such as state health department labs in the U.S., and subsequently to reference centers like the CDC for cholera toxin testing and detailed subtyping. This process is crucial for monitoring trends, identifying outbreaks, and guiding public health interventions for cholera.
