Skip to main page content

• HOME
• Current Issue
• Archive
• Alerts
• About ASM
• Contact us
• Tech Support
• Journals.ASM.org

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hänscheid, T. Articles by Rubio, J. M. Search for Related Content PubMed PubMed Citation Articles by Hänscheid, T. Articles by Rubio, J. M.

 Previous Article  |  Next Article 

Journal of Clinical Microbiology, February 2002, p. 736-737, Vol. 40, No. 2
0095-1137/02/$04.00+0     DOI: 10.1128/JCM.40.2.736-737.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

LETTER TO THE EDITOR

Poor Accuracy of Rapid Diagnostic Tests and Misdiagnosis of Imported Malaria: Are PCR-Based Reference Laboratories the Answer?

Top Letter References Letter  References

 
The recent article by Rubio et al. reports poor accuracy of rapid malaria diagnostic tests (RDTs) and promotes PCR-based reference laboratories to avoid potential misdiagnosis (6). Both points deserve comment.

The authors' reported low sensitivity is mainly due to poor detection of Plasmodium species other than Plasmodium falciparum. Although "pan-specific" antibodies have been included in some RDTs, it is the diagnosis of P. falciparum infection that is crucial for reducing mortality. Here, Rubio et al. confirm the findings of many studies, reporting a sensitivity well above 90% (7). Moreover, an unusually high number of false-positive results are presented, without attempts to identify a reason. For example for an average of more than 17 days, 44.4% of OptiMAL (pLDH-based assay) results were reported to be false positives. However, pLDH is only produced by live parasites, and studies have shown very good correlations with declining parasitemias during follow-up (4). The reported number of pretreatment false positives (>20%) even exceeds numbers reported from studies where the influence of rheumatoid factor on RDT performance was investigated in nonmalarious patients (1).

The authors use this unduly dark picture to justify the need for PCR-based reference laboratories, although they fail to elucidate the clinical usefulness of such tests in the diagnosis of acute malaria. Following their argument of limited accuracy of malaria diagnostic tests, confirmation by a reference center would have to include positive as well as negative samples. Hence, there would be considerable financial and logistic hurdles for such a policy: urgent transport, turnaround time of PCR runs, weekend service, etc. From the authors' country (Spain), a mean annual number of 175 cases per year and for Europe 5,000-8,000 cases per year were reported from 1985 to 1995 (5). However because millions of tourists visit countries where malaria is endemic, each year many of them may present at health service facilities with unspecific symptoms after return, prompting a malaria diagnostic test. For each positive specimen there will be many negative ones. Unfortunately, the feasibility of such a "fast-track" reference laboratory service is not discussed (e.g., in a cost-benefit analysis).

Furthermore, lack of clinical suspicion may be more important in the misdiagnosis of imported malaria than poor performance of laboratory tests. In Canada, more than 50% of malaria cases were clinically not suspected upon first presentation (3). RDTs or PCR-based reference laboratories do not address this problem. Development of common routine laboratory tests that alert to the presence of Plasmodium spp. may be more useful. One example is the detection of hemozoin during automated routine full-blood counts, which allowed the diagnosis of six clinically unsuspected malaria cases in one study (2).

Reference centers play an important role primarily in the posterior confirmation of positive samples, species identification, and comprehensive quality assurance. However, whether the use of presently available RDTs increases the misdiagnosis of imported malaria, as suggested by Rubio et al., remains to be proven by an appropriately designed study. Such a study would have to investigate the routine use of RDTs in normal everyday practice involving non-expert microscopists in peripheral laboratories. Is it not more likely that the judicious use of RDTs would reduce the misdiagnosis of imported malaria in many of these places?

Top Letter References Letter  References

 

1
1. Grobusch, M. P., U. Alpermann, S. Schwenke, T. Jelinek, and D. C. Warhurst. 1999. False-positive rapid tests for malaria in patients with rheumatoid factor. Lancet 353:297.[Medline]
2
2. Hänscheid, T., J. Melo-Cristino, and B. G. Pinto. 2001. Automated detection of malaria pigment in White Blood Cells for the diagnosis of malaria in Portugal. Am. J. Trop. Med. Hyg. 64:290-292.[Abstract]
3
3. Kain, K. C., M. A. Harrington, S. Tennyson, and J. S. Keystone. 1998. Imported malaria: prospective analysis of problems in diagnosis and management. Clin. Infect. Dis. 27:142-149.[Medline]
4
4. Moody, A., A. Hunt-Cooke, E. Gibbet, and P. Chiodoni. 2001. Performance of the OptiMAL malaria antigen capture dipstick for malaria diagnosis and treatment monitoring at the Hospital for Tropical Diseases, London. Brit. J. Haematol. 109:891-894.[CrossRef][Medline]
5
5. Muentener, P., P. Schlagenhauf, and R. Steffen. 1999. Imported malaria (1985-1995): trends and perspectives. Bull WHO 77:560-566.[Medline]
6
6. Rubio, J. M., I. Buhigas, M. Subirats, M. Baquero, S. Puente, and A. Bento. 2001. Limited level of accuracy provided by available rapid diagnostic tests for malaria enhances the need for PCR-based reference laboratories. J. Clin. Microbiol. 39:2736-2737.[Abstract/Free Full Text]
7
7. World Health Organization. 2000. New perspectives. Malaria diagnosis. Report of a Joint WHO/USAID Informal Consultation, 25-27 October 1999. World Health Organization, Geneva, Switzerland. [Online.]

						Thomas Hänscheid* Laboratory of Microbiology Faculdade de Medicina de Lisboa Hospital de Santa Maria P-1600 Lisbon, Portugal, Emilia Valadas Department of Infectious Diseases Hospital de Santa Maria P-1600 Lisbon, Portugal
						* E-mail: t.hanscheid{at}0040fm.ul.pt

Authors' Reply

Top Letter References Letter  References

 
As we report in our study, the percentage of false positives is 24%. Four out of the nine patients that were positive remained positive for an average of 17 days. Some explanations for false positives and negatives can be offered. In the first place, some authors have reported high percentages of false positives related to autoantibody formation (rheumatoid factor and others) for the rapid diagnostic tests (RDTs) (although the numbers for ICT and ParaSight-F tests were higher, than those for OptiMal).

On the other hand, the multiplex PCR was designed from a single-stranded ribosomal DNA gene, a gene with only two copies in asexual stages but that generates multiple copies during asexual schizogony. In exchange, the sexual stages (micro- and macrogametocyte) do not present this multiplicity. This fact and the fact that the PCR was designed with a universal forward primer but four reverse specific primers (one per each Plasmodium species) explain that sexual stages cannot be amplified with exception of cases of very high parasitation with gametocytes. A portion of patients, after treatment with antimalarial drugs, presented with gametocytes in their blood that could persist several (20) days. The gene of pLDH is monocopy without introns, and it is present in chromosome 13. This gene could be expressed in gametocytes and result in a radical cure of patient and presumably to be detected the enzyme by RDTs.

Finally, several patients in this study followed a regimen of chloroquine for malaria prophylaxis (in our case, chloroquine plus proguanil). Chloroquine competes with NADH for binding to the enzyme and to interact specifically with pLDH in the transformation from pyruvate to L-lactate in glycolytic process (2), a fact that could implicate the accumulation of pyruvate and the following enzyme hyperactivity. This fact could have implications in increases or decreases of pLDH in blood.

The majority of trials with RDT's do not include PCR and microscopic diagnosis is performed as the "gold standard." Moreover, a certain number of patients in this study were semi-immune patients with clinical symptoms but with low parasitemias (<150 parasites/µl). Studies evaluating RDTs in nonimmune people (travellers) reveal satisfactory results; however, in the case of low parasitemias the results of sensitivity and specificity decrease notably (3). Actually, in our laboratory, parasitemias of 135, 204, 281, and 273 parasites/µl were diagnosed and/or confirmed during the years 1998, 1999, 2000, and 2001 (up to 18 October), respectively. Only data from the year 2000 for our Unit of Tropical Medicine (Hospital Carlos III) have been reported to the European Network of Imported Infectious Diseases Surveillance 130 malaria imported cases (TropNetEurop; www.tropnet.net). If the confirmed cases reported by us correspond to 30 to 40% of the malaria imported cases from Spain, we think that actually the number of imported cases could be around 400. We are in agreement with Hänscheid that to evaluate the feasibility of a PCR-based reference laboratory, a cost-benefit analysis (including a discussion of financial and logistic hurdles, not to mention the cost of the return of patients at hospital due to misdiagnosis of relapsing infections, as well as the cost of labor absenteeism) is advisable. At present, one of the objectives of the National Institute of Health Carlos III (National Center for Microbiology) is to act as the Reference Center for all microbiological laboratories in the country, with functions of reference, diagnosis and basic research, the two first supported by the State. Moreover, an other function of our laboratory, one that is important to medical entomologists, is to study the receptivity and vulnerability of Spanish vectors in the context of malaria reintroduction hypotheses (4), now especially important, given the increase in Spain of migrant populations from areas where malaria is endemic (Central America and sub-Saharan areas). Actually, the migrant population in Spain corresponds to a population of continuous comings and goings and this fact increase the possibility of malaria recurrence, increasing at the same time the access to health sector, including the blood banks of the hospitals and centers for transfusion. In accordance with these facts, and without discussing the cost-benefit analysis, recently we studied if PCR could be a reference technique for screening units of blood in hospitals and centers of transfusion from donor at risk (1). In conclusion, we suggest the use of RDTs with great caution; at present, these tests alone cannot replace microscopic diagnosis. We also report the experience of the national reference laboratory, where PCR, and other molecular epidemiological markers (e.g., resistance and diversity) are used for confirmation and surveillance of imported malaria in Spain with satisfactory results.

Top Letter References Letter  References

 

1
1. Benito, A., and J. M. Rubio. 2001. Usefulness of seminested polymerase chain reaction for screening blood donors at risk for malaria in Spain. Emerg. Infect. Dis. 7:1068.
2
2. Read, J. A., K. W. Wilkinson, R. Tranter, R. B. Sessions, and R. L. Brady. 1999. Chloroquine binds in the cofactor binding site of Plasmodium lactate dehydrogenase. J. Biol. Chem. 274:10213-10218.
3
3. Ricci, L., I. Viani, G. Piccolo, A. Fabio, A. Calderaro, L. Galati, F. Perandin, L. Vecchia, N. Manca, G. Dettori, A. Turano, and C. Chezzi. 2000. Evaluation of OptiMAL Assay test to detect imported malaria in Italy. N. Microbiol. 23:391-398.
4
4. Romi, R., G. Sabatinelli, and G. Magori. 2001. Could malaria reappear in Italy? Emerg. Infect. Dis. 7:915-919.

						Agustin Benito* Malaria Reference Laboratory Parasitology Department National Center for Microbiology Instituto de Salud Carlos III Ctra. Majadahonda-Pozuelo Km2 28220 Majadahonda Madrid, Spain, Jose Miguel Rubio National Center for Tropical Medicine Instituto de Salud Carlos III 28220 Majadahonda Madrid, Spain
						* E-mail: abenito{at}0040isciii.es

---

Journal of Clinical Microbiology, February 2002, p. 736-737, Vol. 40, No. 2
0095-1137/02/$04.00+0     DOI: 10.1128/JCM.40.2.736-737.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Rougemont, M., Van Saanen, M., Sahli, R., Hinrikson, H. P., Bille, J., Jaton, K. (2004). Detection of Four Plasmodium Species in Blood from Humans by 18S rRNA Gene Subunit-Based and Species-Specific Real-Time PCR Assays. J. Clin. Microbiol. 42: 5636-5643 [Abstract] [Full Text]  

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hänscheid, T. Articles by Rubio, J. M. Search for Related Content PubMed PubMed Citation Articles by Hänscheid, T. Articles by Rubio, J. M.