Malaria self-testing by travellers: opportunitiesand limitations

Tomas Jelinek*

Institute of Tropical Medicine, Spandauer Damm 130, 14050 Berlin, Germany

Received 27 February 2004; accepted 1 March 2004

Available online 19 May 2004

KEYWORDSMalaria; Self-testing;

Dipstick tests

Summary Accurate and timely treatment of imported malaria requires rapid andreliable diagnosis. The availability of a rapid and reliable diagnostic test could improvethe quality of malaria diagnosis in febrile travelers after their return to non-endemiccountries. Rapid and simple immuno-chromatographic tests have been marketed forseveral years. Dipstick tests for malaria diagnosis are still a potentially very usefuladditional tool. Trained laboratory personal have in general no problems in doing thetests. Also, the dipsticks are very valuable tools for use in epidemiological fieldstudies. However, sensitivity and specificity of dipstick tests are still below that oftrained microscopists. Exclusion of malaria should never be based on a negativedipstick test alone. Self-use of dipstick tests for malaria diagnosis by travelers shouldnot be recommended routinely as there is enough evidence that performance andinterpretation of results by the traveler is uncertain. Dipstick tests can only berecommended to travelers for specific situations (i.e. long term stay, far away frommedical assistance, expedition-type travel) after appropriate instruction and training,including a successful performance of the test procedure.q 2004 Published by Elsevier Ltd.

Introduction

Due to the world-wide increase of tourism into, andimmigration from, endemic areas, malaria hasbecome a regularly diagnosed disease in thewestern world. Since incubation periods arecomparatively long and the duration of travel toendemic areas frequently limited to days to a fewweeks, it has been estimated that 90% of infectedtravelers do not develop symptoms until afterreturning home.1 Accurate and timely treatmentof imported malaria requires rapid and reliablediagnosis. Microscopic examination of stained bloodfilms still remains the mainstay of diagnostic

methods. However, correct interpretation ofblood films requires considerable expertise that isnot necessarily available at peripheral medicalcentres in non-endemic countries.2 The availabilityof a rapid and reliable diagnostic test could improvethe quality of malaria diagnosis in febrile travelersafter their return to non-endemic countries.Rapid and simple immuno-chromatographic testshave been marketed for several years. These kitsare based on the detection of circulating para-site-specific antigen in full blood by use of specificantibodies which are bound to a membrane.ICT Malaria Pfw (ICT Diagnostics, Sydney, Australia)and ParasightFR (Beckton-Dickinson, USA) targethistidine-rich protein 2 (HRP2) of Plasmodiumfalciparum whereas OptiMALw (Flow Inc., Portland,Oregon, USA) detects parasite-specific lactate

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Travel Medicine and Infectious Disease (2004) 2, 143–148

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*Tel.: þ49-30-30116-835; fax: þ49-30-30116-888.E-mail address: tomas.jelinek@charite.de (T. Jelinek).

dehydrogenase (pLDH). A test kit capable ofdetecting antigen of P. falciparum and P. vivaxhave also been introduced (e.g. ICT Malaria Pf/Pvw;ICT Diagnostics, Sydney, Australia). The extremelysimple test methodology is intriguing: full blood(be it venous or from a finger prick) is spotted on thetest strip and lysed by a buffer. The resultingsolution moves up the filter to the test area wherespecific antibodies are bound. A few minutes afterwashing with a second buffer, the result is visible asa colorimetric band. Due to the simple handling ofthe test, travelers to malarious areas are advised tocarry the test kit as emergency tool in their luggageand to use it themselves in case they develop afever in a situation where they cannot reachadequate professional help within a safe timelimit. The utilization of this method by travelershas been subject of intensive discussion amongtravel medicine specialists.

Sensitivity and specificity of dipsticktests in various populations

As early as 1999, malaria dipstick tests (or rapiddiagnostic tests, RDTs) were discussed during aWHO workshop that targeted this issue.3,4 Until thebeginning of 2004, Pubmed lists 73 publishedstudies evaluating different commercial malariadipstick tests in different populations. The majority

of these studies was undertaken in endemic regionsin populations who had developed semi-immunityto malaria (Table 1). Some of these studiesused light microscopy as the ‘gold standard’ fordiagnosis, some PCR. The sensitivity for detectingsymptomatic P. falciparum infection rangedbetween 60.4 and 100%. In some instances,a positive dipstick result was obtained even beforeparasite detection by microscopical examination.However, at low parasitemias the sensitivity of alltests decreased as a general rule, especiallyparasite levels below 100/ml caused problems.Some studies show a worrisome tendency ofdipstick tests to remain negative in selectedpatients, even with high parasitemias.5 – 8 Onepossible explanation is variability of the genescoding for the antigens that are used for testdetection causing variation of their protein struc-ture and thus failure of the specific antibodies tobind with the altered antigen. However, a very highparasitemia in itself can inhibit test results: in apatient with 30% parasitemia, a false-negativedipstick test became positive following a 1:10dilution of the blood sample. This fact could beexplained as prozone phenomenon in a blood samplewith very high antigen concentration.6 Specificity ofthe test kits was very high in all studies (87–100%)(Table 1). However, false-positive results arepossible in all dipstick tests used, particularly inpatients with rheumatoid factor9–11 (Table 2).

Table 1 Studies evaluating malaria dipstick tests.

Country Year Populationa Gold standardb Test principle (antigen) Source

HRP2(ParaSightF)

HRP2 (ICT Pf,Makromed)

pLDH (Optimal)

Sens% Spec% Sens% Spec% Sens% Spec%

Uganda 1997 Endemic Microc 71–97d 96 71–100d 92 23France 1997 Travelers Micro 93 98 96 98 24Senegal 1998 Endemic Micro 88 87 89 100 25Belgium 1998 Travelers Micro 95 90 95 89 26Honduras 1998 Endemic Micro 65 65 88e 99e 12Canada 1998 Travelers PCR 94 95 90 97 27Germany 1999 Travelers Micro /PCR 92.5 98.3 88.5f 99.4f 7Indonesia 2000 Local Micro 60.4 97 28Italien 2000 Travelers Micro 94 83 29Europe 2001 Travelers Micro 87.8 99 8Canada 2002 Travelers Micro 97 96 30Italy 2002 Travelers Micro 94.4 94.5 31

a Endemic, symptomatic patients in an endemic area; travelers, symptomatic travelers from malarious areas; local, asymptomaticinhabitatnt of an endemic area.

b Micro, microscopy with thin and thick blood film; PCR, detection of plasmodial DNA by polymerase chain reaction.c Microscopie by local technicians.d Sensitivity in parasitemia from 1–100/ml to 5000/ml.e Study was performed during a falciparum malaria epidemic.f Results exclusively for P. falciparum.

T. Jelinek144

Studies investigating the quality of detection oftertian and quartan malaria by dipstick tests are farless numerous than those with falciparum malaria.All studies on this topic have in common that theirresults are based on very limited case series.In general, detection of P. vivax had a sensitivity of61.5–98% in both test methods with a specificity of96–99%.7,8,12 –14 Depending on the study, the methodfor detection of pLDH (OptiMAL) yielded the lowestand the highest scores for sensitivity. Detection ofP. ovale and P. malariae has not been evaluated insystematic studies. Case reports describe false-negative test result despite microscopically con-firmed diagnosis for both pathogens.15 – 17 Thecommonly low parasitemia in these infectionsseems to deter the diagnostic value of the currentlyavailable dipstick tests.

Self-testing by travelers

Following marketing of the first dipstick tests foruse in medical settings, travelers were detected asa new target group. Due to the extremely simple

handling of the kits that can be used without furtherlaboratory equipment, tests were recommendedfor self-use by febrile travelers. When carrying atest kit to endemic areas, travelers would have thepossibility to perform fast and accurate diagnosis bythemselves without having to rely on locallyavailable infrastructure. Depending on the outcomeof the test, the traveler would then be able to treathimself for falciparum malaria with an emergencymedication (‘stand-by therapy’). A negative testresult would then prevent a traveler fromtaking unnecessary or even potentially harmfulmedication. The utilization of this scenario bytravelers was the subject of intensive debateamong travel medicine specialists. Several studiestried to validate if laymen inexperienced withdiagnostic tools were capable to handle the testkits in a situation of extreme stress and to decidecorrectly for or against treatment upon the result(Table 3).

In a Swiss study, 160 healthy Swiss travelers wereasked prior to travel to perform the ParaSightF testfollowing written instructions. Only 75% ofthe individuals could perform the test correctly.Following a more thorough written and oralinstruction, the performance rate increased to90%. However, even then the interpretation ofresults was unsatisfactory (70.6% correct interpret-ation with 14.1% false-negative results).18 A secondstudy was done within this setting among 98 healthyvolunteers, this time comparing ParasightF and ICTP.f. tests. This investigation demonstrated againhigh level of interpretation and technical problemsin both tests without any difference in theperformance of either. The ICT test fared

Table 2 False-positive results of malaria dipstick tests inpatients with positive rheumatoid factor.9

Type of test Wrong positive results/no. ofpatients testeda (frequency)

ParaSight F 15/92 (16.5%)ICT Malaria P.f. 6/91 (6.6%)OptiMAL 3/91 (3.3%)

a Patients with positive rheumatoid factor and no history orsigns of malaria.

Table 3 Self-testing for malaria by travelers: overview of studies.

Setting Test used n Result Source

Healthy Swiss travelers priorto travel

ParaSight F 160 75% success after oral introduction, 90%following written and oral introduction

18

14% false-negative interpretation of test resultTechnical modification recommended

Healthy Swiss travelers priorto travel

ParaSight F, ICT P.f. 98 Problems with interpretation in lowparasitemia (,0.1%)

19

High rate of false-negative interpretationsTechnical modification recommended

Febrile travelers in Kenya ICT P.f. 98 69% successful test performance withmanufacturer’s test instruction

21

Only 1 in 11 malaria patients performedthe test successfullyIntensive training recommended

Febrile travelers in London ICT P.f. 153 91% successful test performance after intensivetraining and modification of instruction manual

20

100% success in 22 patients with malaria

Malaria self-testing by travellers: opportunities and limitations 145

better for readings and interpretations at higherparasitemias (96 versus 92% correct interpret-ations). The ParasightF was superior at lowerparasitemias (,0.1%) but still not satisfactory(52 versus 11%).19 In a study done in London,153 symptomatic returnees from endemic areaswere asked to perform the ICT P.f. themselves andto interpret the results.20 Patients receiveddetailed instructions on test procedures by thestudy coordinators and were handed a modified andimproved manual. These measures improvedsuccess rates: 91% of study participants were ableto perform the test correctly. All patients withfalciparum malaria ðn ¼ 22Þ were able to diagnosethemselves. The most realistic setting was achievedin a study done in Kenya: febrile travelers whopresented at one of the outpatient departments atthe coast south of Mombasa were recruited for thestudy.21 These patients were asked to performthe test (ICT P.f.) themselves according to themanual provided by the manufacturer, withoutprior instruction. The performance of the studyparticipants was noted by independent observers ona standardized questionnaire, results were checkedagainst microscopy. Only 68% of the patients wereable to perform and to interpret the test correctly.Reasons for problems with test performance arelisted in Table 4. The most important result was that10 out of 11 patients with confirmed falciparummalaria were not able to achieve the diagnosis byusing the dipstick test. When tested bythe attending physician all patients were clearlypositive in the test device.

Conclusions

Accurate and timely diagnosis and treatment offalciparum malaria in non-endemic areas isfrequently complicated by lack of experience onthe side of involved laboratory personal. Diagnostictools based on the dipstick principle for

the detection of plasmodial histidine-rich protein2 (HRP-2) and parasite-specific lactate-dehydro-genase (pLDH), respectively, have become avail-able for the qualitative detection of falciparummalaria. All dipstick tests have the potential ofenhancing speed and accuracy of the diagnosis offalciparum malaria, especially when non-special-ized laboratories are involved. The majority ofstudies evaluating malaria dipstick tests showed ahigh sensitivity and specificity for the detection ofP. falciparum (Table 1). In single cases, malariadiagnosis was achieved 1–2 days faster by dipsticktest than by microscopy. This shows the potentialuse of the method: the infection might have beenoverlooked at a later stage without the dipstick testresult. However, several studies demonstrated thatpatients with high parasitemia remained negative inthe rapid diagnostic tests. Even though reasons forthis are not entirely clear, these reports give aclear message: microscopy must not be neglectedin favour of performing dipstick tests alone.Non-falciparum malaria is not reliably detected bythe available dipstick tests, in particular not inpatients with low parasitemia. Major modificationsand improvements have to be done before dipsticktests might find their place in the diagnosis oftertian or quartan malaria. A ‘lack of false-positiveresults’ has been postulated at least for thedetection of pLDh by OptiMALw.22 This has notbeen confirmed by the overwhelming majority ofstudies (Table 1). False positives were especiallyfrequent in samples with increased rheumatoidfactor (Table 2). It appears that patient withrheumatoid factor have a tendency to react inall immuno-chromatographic test kits for thedetection of malaria antigen.9

Studies investigating the quality of malariaself-testing in travelers to endemic areas aredifficult to construct. Different scenarios havebeen used: asymptomatic travelers pre-travel,symptomatic travelers post-travel, andsymptomatic travelers during travel (Table 3).When original instructions of the manufacturerswere used, performance was invariably disappoint-ing. Quite obviously, all chosen study settingscreated artificial situations where travelersperformed the test in addition to microscopy oreven prior to travel. However, results suggest thatpersons without previous experience in performinglaboratory tests will have problems in stressfulsituation to proceed correctly with a test kit forself-testing (Table 4). Especially the high failurerate in patients with falciparum malaria in therealistic setting of a outpatient clinic in Africapoints towards the problem that patients withfalciparum malaria may simply be too sick to

Table 4 Self-use of rapid tests for malaria diagnosis bytourists: reasons for performance problems (n ¼ 31; multipleentries possible).32

n %

Unable to draw blood (finger prick) 22 71Unable to place the blood dropappropriately on the test kit

8 25.8

No adherence to the recommended waitingperiod (8 min)

12 38.7

Unable to identify the bands indicatingthe test result

18 58.1

Unable to interpret the result 27 87.1

T. Jelinek146

perform self-testing, interpret results and decideon malaria treatment.21 Self-use of dipstick testsfor malaria diagnosis by travelers should not berecommended routinely as there is enoughevidence that performance and interpretation ofresults by the traveler is uncertain. Dipstick testscan only be recommended to travelers for specificsituations (i.e. long term stay, far away frommedical assistance, expedition-type travel)after appropriate instruction and training,including a successful performance of the testprocedure.

With all limitations listed in this article, dipsticktests for malaria diagnosis are still a potentiallyvery useful additional tool. Trained laboratorypersonal has in general no problems in doing thetests. Also, they are very valuable tools for use inepidemiological field studies. It should be empha-sized, though, that sensitivity and specificity ofdipstick tests is still below that of trained micro-scopists. Exclusion of malaria should never be basedon a negative dipstick test alone. Furtherlimitations of the qualitative, not quantitative,test devices are lack of information aboutparasitemia and limited differentiation of mixedinfections with several plasmodial species.The absolute need of thin and thick blood filmmicroscopy in every single patient with suspectedmalaria has not been put aside by the introductionof dipstick tests.

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