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):945-6.
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):301-3.
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
T ite r 1 :1 0
T ite r 1 :2 0 to 1 :8 0
100%
T ite r 1 :1 6 0 o r m o re
90%
A n y d e te cta b le tite r
80%
70%
P ro p o rtio n (% )
• 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
60%
50%
40%
30%
20%
10%
0%
>1
1
2
3
4
5
6 7 8 9
Ag e (ye a rs )
10 11 12 13 14
Wuthiekanun et.al Development of antibodies to Burkholderia pseudomallei during childhood in
melioidosis-endemic northeast Thailand. Am J Trop Med Hyg. 2006;74(6):1074-5.
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, 2010. 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 timeconsuming Requires fresh
reagents each time
• Lacks standardization in the
way the test is done and
interpreted
• Poor diagnostic sensitivity
and specificity