Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (480 page)

   The RPR card test is positive in 75–100% of patients with primary syphilis, 100% with secondary syphilis; 95–100% with latent syphilis, and approximately 75% with late, tertiary syphilis. Specificity is approximately 98%.

   Acute (<6 months’ duration) false-positive tests may occur in acute viral illnesses (e.g., infectious mononucleosis, hepatitis, measles), chlamydia infection, malaria,
Mycoplasma pneumoniae
infection, pregnancy, and recent immunization.

   Chronic (>6 months) false-positive tests may be caused by increased age (>70 years), infection caused by non–
T. pallidum
spirochetal infections, IV drug abuse, medications, and rheumatologic disease and/or underlying disease (e.g., collagen vascular diseases, leprosy, malignancy).

   Treponemal tests

   These tests use
T. pallidum
, or specific
T. pallidum
antigens, to detect antibodies. Particle agglutination and EIA formats are most commonly used. Treponemal tests have been used traditionally to confirm the specificity of positive reactions of nontreponemal assays. However, development of assays adapted for efficient testing of large numbers of patient samples, like EIA assays, has led to increasing use of these assays as primary screening tests.

   Treponemal assays are also used for diagnosis of late latent or tertiary syphilis in untreated patients, when nontreponemal assays may have become nonreactive.

   Treponemal tests usually remain reactive for many years after successful therapy, so these assays are not reliable for measuring response to therapy or to assess the possibility of reinfection.

   
Treponema pallidum
–specific IgG EIA is positive in 90–95% of patients with primary syphilis and 99–100% positive in patients with secondary, latent, or late syphilis.

VIBRIO
INFECTION

   Definition

Vibrio
species are nonfastidious, glucose-fermenting GNBs.
Vibrio cholerae
is the cause of cholera, a severe diarrheal disease. Risk of infection is significant in populations with poor sanitation related to water sources. Transmission is primarily caused by ingestion of contaminated water or poorly cooked seafood. Continued transmission may result by fecal contamination of potable water sources or food. Disruption of potable water sources by natural disaster or civil disruption increases the risk of epidemic disease. Asymptomatic carriage is rare.

   Who Should Be Suspected?

   Young children are most commonly infected and most susceptible to severe infection. After ingestion, symptoms usually begin within 2–4 days. Initial symptoms of nausea, vomiting, and abdominal discomfort are followed by severe diarrhea. Without aggressive rehydration, life-threatening dehydration may ensue, with neuromuscular symptoms, hypoglycemia, acute renal failure, or other complications.