Short report: evaluation of a monoclonal antibody-based latex agglutination test for rapid diagnosis of septicemic melioidosis

A monoclonal antibody (MAb)-based latex agglutination (MAb-LA) test was developed to rapidly identify Burkholderia pseudomallei in hemoculture of patients with septicemic melioidosis. The method was evaluated in a clinical situation on 396 hemocultures positive for bacterial growth, of which 75 cultures were positive for B. pseudomallei by conventional biochemical tests. The sensitivity and specificity of the MAb-LA test were 95% and 100%, respectively. The positive and negative predictive values were 100% and 99%. The method is highly reliable and suitable for rapid diagnosis of septicemic melioidosis, reducing the time normally required from a minimum of 3-4 days by conventional methods to less than 30 hr. Most of these 30 hr are involved in growing up enough bacteria to perform the MAb-LA test, which itself takes only 1 min.     

Evaluation of a newly developed dipstick test for the rapid diagnosis of scrub typhus in febrile patients

Scrub typhus is a potentially fatal, febrile disease prevalent in rural Asia. The etiological agent, Orientia tsutsugamushi, is transmitted to humans by the bite of a larval trombiculid mite. No current diagnostic test is sufficiently practical for use by physicians working in rural areas. A new dipstick test using a dot blot immunoassay format has been developed for the serodiagnosis of scrub typhus. We evaluated this test on 83 patients presenting with acute fever of unknown origin at Maharaj Hospital, a tertiary care medical center in Nakhon Ratchasima, Northeast Thailand. The diagnosis of scrub typhus was confirmed in 30 of these patients (36%) by the indirect immunoperoxidase test. The sensitivity of the test was 87% and its specificity was 94%. The dot blot immunoassay dipstick is accurate, rapid, easy to use, and relatively inexpensive. It appears to be the best currently available test for diagnosing scrub typhus in rural areas where this disease predominates.     

A new latex agglutination test for rapid diagnosis of group A streptococci

A rapid diagnostic test for group A streptococci from throat swabs (Culturette Brand 10-Min Strep ID test of Marion Inc.) was performed in 210 patients with acute pharyngitis. This agglutination test is based on the extraction of streptococcal polysaccharide by nitrous acid and observe agglutination with anti-polysaccharide-coated latex suspension. There was a 95.2% total agreement with a standard culture method and agglutination test and specificity of 93.4%, sensitivity of 96.0% positive predictive value of 90.5% and negative predictive value of 97.3%. From the results of our study, the agglutination test for group A streptococci is of diagnostic value. This new kit would be most useful in out-patient clinics, especially in a small private medical office without culture facilities.     

Multi-laboratory evaluation of a scrub typhus diagnostic kit

Scrub typhus is a major cause of febrile illness throughout the Asia-Pacific region. It is commonly undiagnosed, partly because of the lack of a simple, reliable diagnostic test which can be used in clinical laboratories. The indirect immunoperoxidase technique, configured into a test kit, was provided to technicians who were trained in its use. They used the kit during a 2 year field trial in their respective clinical hospital laboratories throughout Malaysia. In an evaluation using 1,722 consecutive sera tested in those laboratories, the kit was found to have a median sensitivity for IgG detection of 0.85 (range 0.33-0.95), a median specificity of 0.94 (range 0.88-1.00), reproducibility of 0.86, and efficiency of 0.92 when compared to the reference laboratory. In a proficiency survey in which 10 laboratories received 3 coded test samples, all but 2 laboratories had results within 1 dilution of the reference laboratory in quantitating specific IgG, whereas 7 laboratories were within 1 dilution in quantitating IgM. The shelf life of the kit was at least 1 year at 4 degrees C.     

Development of new, broadly reactive, rapid IgG and IgM lateral flow assays for diagnosis of scrub typhus

We evaluated the diagnostic accuracy of two broadly reactive rapid immunochromatographic tests (ICTs) for detection of IgM and IgG against Orientia tsutsugamushi by using archived acute-phase serum samples from 102 patients with laboratory-confirmed scrub typhus, and from 62 archived serum samples from patients with other causes of fever as a negative control. These ICTs were constructed by using a mixture of recombinant proteins: 1) C1, a chimeric protein containing epitopes of the 56-kD antigen from Karp and TA763 strains; 2) Ktr56; and 3) Gmr56. Sensitivities of the ICTs for detection of IgM and IgG were 90.2% (95% confidence interval [CI] = 84.4-96.0%) and 86.3% (95% CI = 80.9-93.8%), respectively. Specificities were 85.5% (95% CI = 73.9-92.2%) and 96.8% (95% CI = 90.3-100%), respectively. Both assays were more sensitive and specific than the standard immune immunofluorescence assay for the early diagnosis of scrub typhus.     

Evaluation of tests for serological diagnosis of scrub typhus

Two specific serological tests, a Dot enzyme immunoassay (EIA) and an immunoglobulin (Ig)M enzyme-linked immunosorbent assay (ELISA) using the 56 kDa antigen and the Weil-Felix test were evaluated for diagnosis of scrub typhus. Sensitivity of 100, 86.5 and 43.5% were observed with Dot EIA, IgM ELISA and Weil-Felix test, respectively. False-positive reactions were observed in patients with falciparum malaria, pulmonary tuberculosis, S. viridans septicemia and typhoid fever using Dot EIA and IgM ELISA. Therefore, although Dot EIA and IgM ELISA are useful in the serodiagnosis of scrub typhus, efforts should be made to rule out other febrile illnesses.     

The latex agglutination test for the diagnosis of meningococcal and haemophilus influenzae meningitis.

103 cerebrospinal fluid (CSF) samples from 55 patients with bacteriologically proven meningitis (caused mainly by Neisseria meningitidis group A and Haemophilus influenzae type b) and from 29 patients with unproved meningitis or other diseases were studied using the latex agglutination (LA) test to demonstrate bacterial antigen in CSF. The tests for N. meningitidis groups A and C and H. ineluenzae type b were found to be rapid, reliable and specific for the serological group of the organism. The demonstration of N. meningitidis group B antigen has not succeeded with the test. Negative results were obtained from culture-positive samples in 4 cases where the bacterial growth was scanty. On the other hand the LA test was clearly positive on 3 occasions in which meningococci did not grow in cultures because of initiated antibacterial therapy or delay before culturing. False-positive results were rare (2 cases). The LA test was found to be at least as sensitive as counterimmunoelectrophoresis in demonstrating bacterial antigens in CSF.     

Early diagnosis of acute myocardial infarction by myoglobin latex agglutination test

Early elevation of the serum myoglobin level in acute myocardial infarction (AMI) has been noted for years. In this study, 39 patients admitted to the Coronary Care Unit with acute chest pain within 72 hours (mean 12 +/- 15 hours) or electrocardiographic changes suspected of acute myocardial infarction had a serum myoglobin latex agglutination test to evaluate its diagnostic accuracy in acute myocardial infarction. Of these 39 patients, 24 had documented acute myocardial infarction as their final diagnosis. By the time of admission, 18 of the 24 cases with infarction had positive myoglobin tests (sensitivity 75%). Of those 15 cases without myocardial infarction, 13 had negative myoglobin tests (specificity 87%). If only those 17 cases admitted within 5 hours of the onset of chest pain were analyzed, the serum myoglobin test became positive in 8 of 10 cases with documented AMI but the 2 cases with negative results turned positive 2 hours later (sensitivity 80% to 100%). Due to the fact that myoglobin tests were negative in all other 7 cases without infarction, the specificity was 7/7 (100%). In contrast, the creatine phosphokinase isoenzyme study was positive only in 3 of these 10 patients with documented AMI in the first blood sample taken during admission. In conclusion, the serum myoglobin latex agglutination test is a quick and reliable method that helps in the early diagnosis of acute myocardial infarction.     

Comparison of a rapid diagnostic test and microimmunofluorescence assay for detecting antibody to Orientia tsutsugamushi in scrub typhus patients in China

ObjectiveTo evaluate the detection of IgM and IgG antibodies to Orientia tsutsugamushi (O. tsutsugamushi) by rapid diagnostic test (RDT) and microimmunofluorescence assay (mIFA).MethodsRDT using a mixture of recombinant 56-kDa proteins of O. tsutsugamushi and mIFA assay were performed on 20 patients from Fujian and 13 patients from Yunnan Province, and 82 sera samples from healthy farmers in Anhui Province and Beijing City in 2009. Comparison of the RDT and mIFA assay was performed by using X² test and the P level of <0.05 was considered to be significance.ResultsAmong these 82 normal sera samples, the specificity of RDT was 100% for both IgM and IgG tests. In 33 samples from patients with scrub typhus, 5 cases were positively detected earlier by RDT than by mIFA in IgM test, and 2 cases were positive in IgG test. Sensitivities of RDT were 93.9% and 90.9% for IgM and IgG, respectively. The sensitivity of combination test of IgM and IgG was 100%. Geometric mean titer diluted sera from confirmed cases by IFA and RDT assay were 1:37 vs. 1:113 (P<0.001) in IgM test and 1:99 vs. 1:279 (P<0.05) in IgG test.ConclusionsRDT is more sensitivite than mIFA in the early diagnosis of scrub typhus and it is particularly applicable in rural areas.     

A rapid latex agglutination assay for the determination of plasma fibrinogen

A monoclonal antibody to intact fibrinogen has been employed to develop a rapid latex agglutination assay for the estimation of plasma fibrinogen. The monoclonal antibody, 45J, recognizes an epitope located in the mid-section of the carboxy terminal end of the A alpha-chain. The epitope is destroyed by plasmin digestion of fibrinogen and there is no immunoreactivity with soluble cross-linked fibrin degradation products. The latex agglutination assay developed with the antibody is unaffected by aprotinin or anticoagulants, such as citrate, heparin or EDTA. When this method was compared with functional clotting assays, excellent correlation was observed with normal and pathological samples. After sample collection and dilution, the assay takes just two minutes to complete. Therefore, this procedure offers a simple and rapid assay for the measurement of intact fibrinogen in plasma.     

Evaluation of a urinary antigen-based latex agglutination test in the diagnosis of kala-azar in eastern Nepal

BACKGROUND: We evaluated the diagnostic accuracy as well as the reproducibility of the urine latex agglutination test 'KAtex' in the diagnosis of kala-azar in patients recruited at a tertiary care centre in Dharan, Nepal, between November 2000 and January 2002. METHODS: All patients presenting with fever of 2 weeks or more and splenomegaly were consecutively enrolled. Bone marrow and--if negative--spleen aspirates were examined for Leishmania donovani. Serum and urine samples were taken in duplicate for the Direct Agglutination Test (DAT) and KAtex. The reference laboratory determined sensitivity and specificity of KAtex. Reproducibility between both laboratories was assessed. RESULTS: KAtex was performed on urine from 155 parasitologically confirmed kala-azar and 77 non-kala-azar cases (parasitology and DAT-negative). KAtex showed a sensitivity of 47.7% (74/155, 95% CI: 39.7-55.9) and a specificity of 98.7% (76/77, 95% CI: 93.0-100.0). Reproducibility of KAtex showed a kappa of 0.684 (P < 0.001, n = 232). CONCLUSION: KAtex evaluation showed high specificity, low sensitivity and moderate reproducibility. A urine test for kala-azar could become a real breakthrough in kala-azar management if its reproducibility and sensitivity could be further improved.     

A rapid latex agglutination test for the detection of anti-cysticercus antibodies in cerebrospinal fluid (CSF)

Simple and rapid latex-based diagnostic tests have been used for detecting specific antigens or antibodies in several diseases. In this article, we present the preliminary results obtained with a latex agglutination test (LAT) for diagnosing neurocysticercosis by detection of antibodies in CSF. A total of 43 CSF samples were assayed by the LAT: 19 CSF samples from patients with neurocysticercosis and 24 CSF samples from patients with other neurologic disorders (neurosyphilis, n = 8; neurotoxoplasmosis, n = 3; viral meningitis, n = 4, chronic headache, n = 9). The LAT exhibited 89.5% sensitivity and 75% specificity. The use of LAT seems to be an additional approach for the screening of neurocysticercosis with advantage of simplicity and rapidity. Further studies could be performed using purified antigens and serum samples.     

Rapid serodiagnosis for leprosy--a preliminary study on latex agglutination test

In this study, we have developed two latex agglutination tests (LATs) with phenolic glycolipid-I (PGL-I) and natural disaccharide-octyl-bovine serum albumin (ND-O-BSA) as antigens in 110 leprosy patients (LL = 30, BL = 30, BT = 30, and TT = 20), 50 tuberculosis cases, and 30 normal controls. These two LATs were compared with corresponding ELISAs (ND-O-BSA ELISA and PGL-I ELISA) and analyzed by the chi-squared test. There were no significant differences between the two LATs (PGL-I LAT and ND-O-BSA LAT) and their corresponding ELISAs. There was an increase in the proportion of positive cases detectable which coincided with the clinical classification of leprosy, i.e., lepromatous cases were more likely to be positive than tuberculoid cases. LATs are more simple and rapid than ELISAs and have high sensitivity (77% in ND-O-BSA LAT, 80.5% in PGL-I LAT) and specificity (99% in both LATs). LATs may become useful tools for the immunodiagnosis of leprosy in the field. The stability and repeatability of LATs are discussed in detail.