CHOLERA : CLINICAL ASPECTS
Typical cholera has a rapid onset, beginning with abdominal fullness and discomfort, rushes of peristalsis, and loose stools. Vomiting may also occur. The stools quickly be- come watery, voluminous, almost odorless, and contain mucus flecks, giving it an ap- pearance called rice-water stools. Neither white blood cells or blood are present in the stools, and the patient is afebrile. Clinical features of cholera result from the extensive fluid loss and electrolyte imbalance, which can lead to extreme dehydration, hypoten- sion, and death within hours if untreated.
The initial suspicion of cholera depends on recognition of the typical clinical features in an appropriate epidemiologic setting. A bacteriologic diagnosis is accomplished by isola-tion of V. cholerae from the stool. The organism grows on common clinical laboratory media such as blood agar and MacConkey agar, but its isolation is enhanced by the use of a selective medium (thiosulfate-citrate-bile salt-sucrose agar). Once isolated, the or-ganism is readily identified by biochemical reactions. Outside cholera endemic areas, the selective medium is not routinely used for stool cultures, so clinical laboratories must be alerted to the suspicion of cholera.
The outcome of cholera is dependent on balancing the diarrheal fluid and ionic losses with adequate fluid and electrolyte replacement. This is accomplished by oral and/or in-travenous administration of solutions of glucose with near physiologic concentrations of sodium and chloride and higher than physiologic concentrations of potassium and bicar-bonate. Exact formulas are available as dried packets to which a given volume of water is added. Oral replacement, particularly if begun early, is sufficient for all but the most severe cases and has substantially reduced the mortality from cholera. Antimicrobial therapy plays a secondary role to fluid replacement. Tetracyclines shorten the duration of diarrhea and magnitude of fluid loss. Trimethoprim – sulfamethoxazole and erythromycin are alternatives for use in children and pregnant women.
Epidemic cholera, a disease of poor sanitation, does not persist where treatment and disposal of human waste is adequate. Because good sanitary conditions do not exist in much of the world, secondary local measures such as boiling or chlorination of water during epidemics are required. The cases associated with crustaceans can be prevented by adequate cooking (10 minutes) and avoidance of recontamination from containers and surfaces. Vaccines prepared from whole cells, lipopolysaccharide, and CT B subunit have been disappointing, providing protection that is not long-lasting. Current interest includes live attenuated vaccine strains because of their potential to stimulate the local sIgA immune response.