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Comparison of two antigen detection techniques in a primate model of Haemophilus influenzae type b infection
Abstract:
Rapid diagnosis of Haemophilus influenzae type b meningitis is possible using immunological tests for capsular antigen (polyribophosphate, PRP), such as countercurrent immunoelectrophoresis (CIE) and latex particle agglutination (LPA). We compared two tests in monkeys with evolving, serially quantitated H. influenzae type b bacteremia (n = 23) and meningitis (n = 21). In vitro, the LPA test was sensitive to 0.5 ng of PRP/ml of saline, and the CIE test was sensitive to 1.0 ng/ml; in serum, however, CIE detected 5.0 ng of PRP/ml, whereas the sensitivity of LPA was unchanged. LPA detected PRP earlier in the course of bacteremia (mean, 12 h after onset; range, 4 to 36 h) than did CIE (mean, 45 h; range, 4 to 168 h) (P less than 0.01). A positive LPA test required greater than or equal to 100 bacteria per ml of blood, whereas CIE required greater than or equal to 1,000/ml. PRP accumulated with continuing blood stream infection, aiding detection of low-grade bacteremia. LPA detected antigen in cerebrospinal fluid (CSF) earlier in the course of meningitis and at a lower bacteria density than did CIE. Both methods detected antigen reliably with greater than or equal to 1,000 bacteria per ml of CSF. A close correlation existed between CSF concentrations of capsular antigen and bacteria (r = 0.90, P less than 0.001). We conclude that the LPA method permits earlier diagnosis of H. influenzae type b infection in part because of its greater sensitivity.
Insights
The latex particle agglutination (LPA) test offers earlier diagnosis of Haemophilus influenzae type b meningitis compared to countercurrent immunoelectrophoresis (CIE) due to its superior sensitivity in detecting the capsular antigen (polyribophosphate, PRP).
Area of Science:
- Microbiology
- Immunology
- Infectious Diseases
Background:
- Rapid diagnosis of Haemophilus influenzae type b (Hib) meningitis is crucial for effective treatment.
- Immunological tests detecting capsular antigen (polyribophosphate, PRP) like CIE and LPA are used for diagnosis.
Purpose of the Study:
- To compare the diagnostic performance of latex particle agglutination (LPA) and countercurrent immunoelectrophoresis (CIE) for Haemophilus influenzae type b (Hib) infection.
- To evaluate the sensitivity and speed of antigen detection in bacteremia and meningitis models.
Main Methods:
- Comparison of LPA and CIE tests in monkeys with experimentally induced Hib bacteremia and meningitis.
- Serial quantification of polyribophosphate (PRP) antigen in blood and cerebrospinal fluid (CSF).
- In vitro and in vivo sensitivity testing of both immunological assays.
Main Results:
- LPA demonstrated higher sensitivity in vitro (0.5 ng/ml) and in serum compared to CIE.
- LPA detected PRP antigen earlier in bacteremia (mean 12h vs 45h for CIE) and at lower bacterial densities (100/ml vs 1000/ml).
- LPA also enabled earlier antigen detection in CSF during meningitis and correlated closely with bacterial load.
Conclusions:
- The LPA test is more sensitive and allows for earlier diagnosis of Hib meningitis than the CIE test.
- LPA's enhanced sensitivity is attributed to its ability to detect lower concentrations of PRP antigen.
- These findings support LPA as a valuable tool for rapid Hib infection diagnosis.