Assessment of three new parasite lactate Assessment of three new parasite lactate dehydrogenase (pan-pLDH) tests for dehydrogenase (pan-pLDH) tests for diagnosis of uncomplicated malariadiagnosis of uncomplicated malaria   

Fogg CL1, Nabasumba C1, Twesigye R1, Batwala V2, Piola P1, Kiguli J1, Mutebi F1, Hook C3, Guillerm M4, Moody A4, Guthmann J-P1

1Epicentre, 2Mbarara University of Science and Technology, 3MSF - Malaria Working Group, 4MSF – Access Campaign

 

Background Microscopy = recommended method for malaria

diagnosis: Trained staff Quality equipment Supervision

Rapid diagnostic tests (RDT) are useful for malaria diagnosis where high standard microscopy is not available: Easy to use Simple to interpret

Study rationale Most common RDT detect Histidine Rich

Protein 2 (HRP2), i.e. Paracheck®

HRP2 tests have 2 major drawbacks: Only detect P. falciparum Remain positive for weeks after treatment

New RDTs detect parasite Lactate DeHydrogenase (pLDH): Identify all plasmodium species Become negative quickly after treatment

The study assessed 3 new pLDH tests

Objectives Primary objective

Measure validity of 3 pLDH tests and that of Paracheck ®

Secondary objectives Measure % of positive tests after effective

treatment Ease of use Measure inter-reader reliability

Methods I: Inclusion Screening at OPD of Mbarara hospital

Inclusion: symptoms of simple malaria signed informed consent

Two age groups: “under 5” and “5 and above”

Sample size: 400 patients (200 blood smear [+] and 200 blood smear [-])

All tests were double read, blinded and compared to microscopy

Reading of blood smears controlled in Thailand

Methods II: Tests performed

1 2 3 4

Methods III: Follow-Up Patients:

Positive BS on D0 OR At least 1 positive RDT on D0

Positive BS on D0 treated with Coartem®

Pregnant women were excluded

Procedures on D3 & D14: Clinical examination Blood smear All tested RDTs

Methods IV: Outcomes Validity:

Sensitivity: % of true positives Specificity: % of true negatives

Percentage of RDTs remaining positive at D3 & D14

Inter-reader reliability: kappa coefficient (above 0.80 was considered « Good Agreement»)

Ease of use determined by a score

Results (I): ValiditySensitivity(N=248)

Specificity(N=212)

Paracheck® 94% [90.2 - 96.6]

87.3%[82.0 – 91.4]

Vistapan® 91.9%[87.8 – 95]

89.6%[84.7 – 93.4]

Carestart® 95.6%[92.2 – 97.8]

91.5%[86.9 – 94.9]

Parabank® 84.7 %[79.6 – 88.9]

94.3%[90.3 – 97.0]

Results (II): Sensitivity by group

Parasite density: Sensitivity decreased with parasitemia Parasitaemia <100 parasites/µL (from 41.9%

[Parabank] to 67.7% [Carestart])

Age group: Sensitivity increased in under 5’s From 95.3% [Parabank] to 97.7% [Vistapan/Carestart])

Results (III): Positive tests after treatment

Day 3 Day 14

pLDH

Parabank ® 17.8%[12.5 – 23.1]

4.6%[1.7 – 7.5]

Vistapan ® 36.1%[29.7 – 42.5]

8.9%[5.1 – 12.7]

Carestart ® 42.5%[36.1 – 48.9]

9.5%[5.6 – 13.4]

HRP2 Paracheck ® 86.2%[81.7 – 90.7]

69.7%[63.1 – 75.7]

Results (IV): Reliability

Kappa above 0.9 for inter-reader reliability for all tests

Results (V): Ease of use

CHARACTERISTIC Paracheck Vistapan Carestart Parabank

I Performance 21 30 18 21

II Safety 7.5 7.5 15 7.5

III Result stability 5 5 5 5

IV Interpretation 30 21 21 30

V Storage 20 20 20 12

TOTAL (/100) 83.5 83.5 79 75.5

Conclusions

Carestart and Vistapan best tests: Parabank (poorly sensitive) Paracheck (high % of positives at D14)

Carestart and Vistapan could replace Paracheck for malaria diagnosis in sub-Saharan Africa

However, pLDH tests have slightly higher costs ($0.6 to $0.7 vs $0.45 for Paracheck)

Acknowledgements

Thanks to:

Mbarara University of Science & Technology Study team and patients in Mbarara. Malaria Working Group, MSF. Access to Essential Medicines Campaign, MSF. The test manufacturers. Shoklo Malaria Research Unit.

Validity detailsSensitivity(N=248)

Specificity(N=212)

PARACHECK 94% (n=233)[90.2 - 96.6]

87.3% (n=185)[82.0 – 91.4]

VISTAPAN 91.9% (n=228)[87.8 – 95]

89.6%(n=190)[84.7 – 93.4]

CARESTART 95.6% (n=237)[92.2 – 97.8]

91.5% (n=184)[86.9 – 94.9]

PARABANK 84.7 % (n=210)[79.6 – 88.9]

94.3% (n=200)[90.3 – 97.0]

Positive Tests D3/D14 details

Day 3 Day 14

pLDH

Parabank 17.8%[12.5 – 23.1](36/202)

4.6%[1.7 – 7.5](9/196)

Vistapan 36.1%[29.7 – 42.5](79/219)

8.9%[5.1 – 12.7](19/213)

Carestart 42.5%[36.1 – 48.9](97/228)

9.5%[5.6 – 13.4](21/221)

HRP2 Paracheck 86.2%[81.7 – 90.7](193/224)

69.7%[63.1 – 75.7](152/218)

PPV & NPVPARACHECK VISTAPAN CARESTART PARABANK

Sensitivity 94%* 91.9%* 95.6%* 84.7 %

[90.2 - 96.6] [87.8 – 95] [92.2 – 97.8] [79.6 – 88.9]

Specificity 87.3% 89.6% 91.5%* 94.3%*

[82.0 – 91.4] [84.7 – 93.4] [86.9 – 94.9] [90.3 – 97.0]

PPV 89.6% 91.2%* 92.9%* 94.6%*

[85.3 – 93] [87 – 94.4] [89.1 – 95.8] [90.7 – 97.2]

NPV 92.5%* 90.5%* 94.6%* 84.0%

[87.9 – 95.7] [85.7 – 94.1] [90.6 – 97.3] [78.7 – 88.4]

Methods V: External Quality Control External quality control performed at

Shoklo Malaria Research Unit, Thailand

Randomly selected 145 positive slides and 145 negative Day 0 slides.

Results (VI): Quality control of slides

Number of discordances: 7 out of 145 (<5%)