Clinical microbiology laboratories have a critical role in the surveillance of Vibrio
infections and the early detection of Vibrio
outbreaks. In our survey of Gulf Coast laboratories, the majority (85%) of stools were cultured in laboratories where TCBS agar was available, but only a small percentage (22%) of stools in these laboratories were screened for Vibrio
using TCBS agar. Furthermore, there was no evidence of seasonal use of TCBS agar, even though Vibrio
infections are more common during the warmer months (10
infections are reportable in each of the five states in this survey; however, 24% of microbiology supervisors in laboratories that performed stool cultures did not know that isolation of Vibrio
was reportable in their state. These findings suggest that a marked burden of Vibrio
illness (sporadic illness as well as outbreaks) may go undetected in those states.
Cost was perceived by 43% of laboratories to be a barrier to the routine use of TCBS agar in screening for Vibrio
spp. Cost per positive culture has been used as a determinant of the practicality of routine laboratory screening for enteric pathogens, such as Escherichia coli
). Cost per positive culture in this survey was estimated by taking the number of stool samples routinely screened using TCBS during the month of June 1998 in laboratories that met the following criteria: (i) screening all stools for Vibrio
with TCBS agar and (ii) isolating a Vibrio
organism from TCBS agar. To approximate screening for sporadic Vibrio
infections, Texas laboratories were excluded from this cost estimate. The number of stool samples screened during June was multiplied by the cost per TCBS agar plate ($1.50) and then divided by the number of culture-confirmed Vibrio
infections identified by these laboratories. Using this formula, cost per positive culture was $72.00. The average treatment cost per culture-positive V. parahaemolyticus
infection is $1,000.00 (9
). If laboratories were to focus their surveillance for Vibrio
by routinely screening all stool samples with TCBS agar during the summer months, more Vibrio
infections would be detected, thus reducing cost per positive culture.
Alternatively, laboratories could reduce the cost and make more efficient use of TCBS agar by having access to patient's food histories, particularly during the warmer months. Only 13% of laboratories reported obtaining a food history from the physician. Physicians' knowledge of risk factors associated with various enteric infections is an important clinical diagnostic tool (5
). Increased awareness among physicians regarding Vibrio
infections may increase the likelihood of obtaining a food history, as well as increase the number of requests for stool cultures to be screened for Vibrio
. A food history indicating recent seafood exposure provided to the microbiologist may help those in the laboratory choose which stool specimens to test with TCBS agar, even if a specific request was not made.
The use of commercial systems for the identification of Vibrio
species needs further evaluation. Commercial biochemical identification systems such as Vitek (Vitek Systems, Inc., Hazelwood, Mo.) originated in the 1960's. These systems are capable of identifying gram-negative bacteria, gram-positive bacteria, yeasts, and anaerobic organisms. In 1989, the gram-negative identification test kit for the Vitek system was expanded to include members of the Vibrio
). In one study, the Vitek system was evaluated for its ability to correctly identify 212 Vibrio
isolates, compared with conventional biochemicals and another commercial system, the API20E (Analytab Products, Plainview, N.Y.) (S. Farnham, N. Moss, and J. Scott, Abstr. 89th Annu. Meet. Am. Soc. Microbiol. 1989, abstr. C-263, 1989). The overall correlation of Vitek with the reference identification systems was 95%. Another study used 60 Vibrio
isolates to compare three different commercial systems against the use of standard biochemicals; only one, the API20E, was considered to be a valid system for use in the identification of the more commonly isolated members of the family Vibrionaceae
). Our limited survey indicated that using other enteric agars in conjunction with commercial biochemical identification systems to identify Vibrio
spp. yielded accurate results only 50% of the time. However, when TCBS agar was used in conjunction with a commercial system, 88% of isolates were correctly identified. This finding suggests that until further evaluation of a large number of Vibrio
strains is completed, TCBS agar should be used for primary laboratory isolation of Vibrio
species, with the use of commercial systems for species identification.
Unfortunately, even though Vibrio
infections continue to occur in coastal areas (6
), the percentage of Gulf Coast laboratories routinely screening stools for Vibrio
with TCBS agar was significantly lower (20% versus 30%) than that found in one recent national laboratory survey (20
) and approximately the same as that from another national laboratory survey (T. J. Van Gilder, D. Christensen, S. Shallow, T. R. Fiorentino, S. Desai, M. Pass, J. Wicklund, C. Stone, and M. Cassidy, Abstr. 99th Gen. Meet. Am. Soc. Microbiol., abstr. C-419, 1999). Furthermore, the majority (53%) of Gulf Coast laboratories that processed stool specimens on-site never used TCBS agar. Finally, there was no evidence of seasonal use of TCBS agar in our survey. Taken together, these data indicate that TCBS agar is underused in Gulf Coast states.
Surveillance data and recent outbreaks of V. parahaemolyticus
) indicate that Vibrio
infections continue to be an important cause of gastroenteritis in coastal areas of the United States; therefore, clinicians, laboratories, and health authorities should remain vigilant in their diagnosis, detection, and surveillance of these organisms. Clinicians should consider requesting a stool culture for Vibrio
when a patient presents with gastroenteritis and a recent history of raw seafood consumption, and they should make this patient's history available to the clinical laboratory. Clinical laboratories should provide clinicians with a specimen submission form that requests food history information, as a guide to clinical laboratory diagnosis. To enhance detection of vibrios, clinical laboratories should encourage the appropriate use of transport media for sample submission, consider screening all stools with TCBS agar during the warmer months (May to October), when Vibrio
infections are most likely to occur, and use TCBS agar in conjunction with commercial biochemical identification systems for Vibrio
species identification. Any V. cholerae
isolates identified should be referred to the state public health laboratory for confirmation, serotyping, and toxin testing. State health authorities in Gulf Coast states should remind clinical laboratories and physicians that Vibrio
infections are reportable and should encourage increased stool culturing for Vibrio
during the warmer months in laboratories where TCBS agar use is not routine. Taken together, these recommendations would enhance surveillance for Vibrio
infections, resulting in earlier detection and recognition of sporadic cases and outbreaks.