Presentation on theme: "Use of the IHA: pros and cons Sharon Peacock University of Cambridge & Mahidol University."— Presentation transcript:
Use of the IHA: pros and cons Sharon Peacock University of Cambridge & Mahidol University
Applications 1.Used in research studies to: - biomarker for presence of Bp/melioidosis - Define prevalence of seropositivity 2.Detect seroconversion after accidental exposure 3.Detect seroconversion after deliberate exposure 4.Diagnosis of melioidosis
Research: surrogate for melioidosis Wuthiekanun V, et al. Melioidosis in Myanmar: forgotten but not gone? Am J Trop Med Hyg. 2006;75(5): Serologic survey of adults living in Myanmar. Antibodies detectable by IHA in 757 (78%); 69 (7%) had IHA titer > or =1:160 Wuthiekanun V, et al. Burkholderia pseudomallei antibodies in children, Cambodia. Emerg Infect Dis. 2008;14(2): Serologic survey of 968 children living in Siem Reap, Cambodia. Antibodies detected by IHA in 16%. Values ranged from 10 to 10,240 (median 10, interquartile range [IQR] 20–640). Organism was isolated from 30% of rice paddies in the surrounding vicinity. No report of cases of melioidosis.
Prevalence of seropositivity Wuthiekanun et.al Development of antibodies to Burkholderia pseudomallei during childhood in melioidosis-endemic northeast Thailand. Am J Trop Med Hyg. 2006;74(6): Cross-sectional serological survey of 2,214 children in NE Thailand IHA titre Birth to 14 years Sharp rise in detectable antibodies from birth to 4 years Reactivity in 60-70% of children thereafter
Prevalence of seropositivity Varies between different regions What do these differences mean? Cross-reactivity?
IHA testing after accidental exposure Protocol devised by panel of experts Serum samples taken on d 1 and weeks 1, 2, 4 and 6 Baseline (pre-employment) and first 2 samples (d 1 & w 1) tested at 1 week Repeat testing with all samples on weeks 2, 4 and 6 Any reproducible rise between two samples is an indicator of seroconversion from exposure Believe titre of 1:40 upwards. Noise below that? Verify positives by repeat testing Peacock SJ, Schweizer HP, Dance DA, Smith TL, Gee JE, Wuthiekanun V, DeShazer D, Steinmetz I, Tan P and Currie BJ. Online Report: Management of Accidental Laboratory Exposure to Burkholderia pseudomallei and B. mallei. Emerg Infect Dis. 2008; 14(7):e2.
IHA testing after deliberate exposure Workshop held prior to WMC 2010 IHA (or serological testing in general) not mentioned in published report Group considered that serological testing would not be done in the event of a deliberate release Lipsitz R, Garges S, Aurigemma R, Baccam P, Blaney DD, Cheng AC, Currie BJ, Dance D, Gee JE, Larsen J, Limmathurotsakul D, Morrow MG, Norton R, O'Mara E, Peacock SJ, Pesik N, Rogers LP, Schweizer HP, Steinmetz I, Tan G, Tan P, Wiersinga WJ, Wuthiekanun V, Smith TL. Workshop on Treatment of and Postexposure Prophylaxis for Burkholderia pseudomallei and B. mallei Infection, Emerg Infect Dis. 2012;18:e2.
IHA testing for diagnostic purposes YES Presence of antibodies indicates exposure Presence of antibodies does not confirm active infection Absence of antibodies does not rule out diagnosis Diagnostic titre? 1:40/1:160 May have pre-existing antibodies to B. pseudomallei Presence of antibodies indicates exposure Presence of antibodies does not confirm active infection Absence of antibodies does not rule out diagnosis Diagnostic titre? 1:40/1:160 Cheng AC, O'brien M, Freeman K, Lum G, Currie BJ. Indirect hemagglutination assay in patients with melioidosis in northern Australia. Am J Trop Med Hyg. 2006;74(2):330-4.
IHA in Australia (Bart) Not melioid unless there is a positive culture Never use rising IHA titres for diagnosis as it is so variable, even when tested in parallel Don’t get distracted by IHA – emphasis on getting all the correct cultures onto Ashdown agar If the test is done and shows a high IHA titre, look harder for active infection High titre, culture -ve and not septic, or responds to initial non-specific Tx, don’t Tx as melioid but advise for melioid to be considered in future and reculture if gets fevers/unwell again etc.
IHA Thailand (Direk) Clinicians in Thailand use IHA Diagnostic titre: single cutoff of admission sample (>=1:160) and/or fourfold rising Better to stick with culture Advisory group to ministry of public health Thailand to re-write the diagnosis criteria for melioidosis to be culture only?
Summary of applications Post-exposure investigation Research, surrogate for presence of Bp and melioidosis
Pros The only test with sufficient evidence to allow use for post-exposure testing Other tests such as ELISA lack clinical validation Cons Requires skill and training Few people in the world with knowledge Laborious and time- consuming Requires fresh reagents each time Lacks standardization in the way the test is done and interpreted Poor diagnostic sensitivity and specificity