Letters to the Editor - March 15, 2000 - American Academy of Family Physicians

Letters to the Editor

Rapid 'Dipstick' Assays for the Detection of Malaria

TO THE EDITOR: I enjoyed the recent article "Case Studies in International Travelers,"¹ in which Dr. Kitchen discussed several clinical vignettes of illnesses, including malaria, in travelers returning to the United States. Microscopy of serial blood smears to detect the presence of the malaria parasites (plasmodium species) continues to be the "gold standard" for clinical diagnosis because it allows estimation of parasitemia, distinction between parasite growth stages and identification of the four different plasmodium species of malaria. However, the article did not address the recent advances in rapid "dipstick" assays to detect malaria. Several commercially available immunochromatographic antigen detection assays are available (see the accompanying table). These assays have been used in various clinical settings in North America and endemic regions.

Rapid "Dipstick" Blood Tests for Detection of Malaria

Assay (company; contact address)
Plasmodium species identified
Parasite antigen detected
Sensitivity (%)
Specificity (%)

OptiMAL^4,5
Flow Inc., Portland, OR
Web site: http://www.malariatest.com P. falciparum Parasite lactate dehydrogenase 88-91 (P.f) 92-99 (P.f)

P. vivax 94 (P.v) 100 (P.v)

ICT Malaria P.f/P.v⁶
AMRAD ICT, Sydney, NSW, Australia
Web site: http://www.amrad.com.au P. falciparum HRP-2 95 (P.f) 89 (P.f)

P. vivax 75 (P.v) 95 (P.v)

PATH Falciparum Malaria IC Strip²
Quorum Diagnostics, Vancouver, Canada
E-mail: info@path.org P. falciparum HRP-2 96 99

Parasight-F³
Becton Dickinson Tropical Diagnostics, Sparks, MD
Web site: http://www.bdms.com P. falciparum HRP-2 94 95

ICT Malaria P.f³
AMRAD ICT, Sydney, NSW, Australia
Web site: http://www.amrad.com.au P. falciparum HRP-2 90 97

P.f = Plasmodium falciparum; P.v = Plasmodium vivax; HRP-2 = histidine-rich protein 2.
Information from references 2, 3, 4, 5 and 6.

The older "dipstick" tests (Parasight-F, ICT Malaria P.f and PATH Falciparum Malaria IC Strip) detect only Plasmodium falciparum infection. All three assays detect histidine-rich protein 2, an antigen expressed only by P. falciparum trophozoites.^2,3 However, the two newer tests (the OptiMAL assay, and the ICT Malaria P.f/P.v assay) have the advantage of detecting infection with P. falciparum or Plasmodium vivax. The OptiMAL assay detects parasite lactate dehydrogenase (pLDH) and can distinguish between P. falciparum and P. vivax because of antigenic differences between their pLDH isoenzymes.^4,5 Because only live parasites produce pLDH, this test can be of clinical relevance because it distinguishes between living (current infection) and dead parasites (recently treated infection). The ICT Malaria P.f/P.v test detects histidine-rich protein 2 found only in P. falciparum and panmalarial antigens found in P. vivax, again, allowing the two species to be differentiated.⁶

Although some of these assays are relatively expensive and are awaiting final labeling approval from the U.S. Food and Drug Administration, they can provide excellent diagnostic aids for family physicians caring for immigrants or travelers who have recently returned from malarious areas, as well as for physicians providing health care to persons in developing countries--especially if a trained microscopist is not readily available.

MATTHEW J. THOMPSON, M.B.CH.B., D.T.M.H.
University of Washington
Department of Family Medicine
Seattle, WA 98195-4696

REFERENCES

Kitchen LW. Case studies in international travelers. Am Fam Physician 1999;60:471-4.

Mills CD, Burgess DC, Taylor HJ, Kain KC. Evaluation of a rapid and inexpensive dipstick assay for the diagnosis of Plasmodium falciparum malaria. Bull World Health Organ 1999;77:553-9.

Pieroni P, Mills CD, Ohrt C, Harrington MA, Kain KC. Comparison of the ParaSight-F test and the ICT Malaria Pf test with the polymerase chain reaction for the diagnosis of Plasmodium falciparum malaria in travellers. Trans R Soc Trop Med Hyg 1998;92:166-9.

Palmer CJ, Lindo JF, Klaskala WI, Quesada JA, Kaminsky R, Baum MK, et al. Evaluation of the OptiMAL test for rapid diagnosis of Plasmodium vivax and Plasmodium falciparum malaria. J Clin Microbiol 1998;36:203-6.

Cooke AH, Chiodini PL, Doherty T, Moody AH, Ries J, Pinder M. Comparison of a parasite lactate dehydrogenase-based immunochromatographic antigen detection assay (OptiMAL) with microscopy for the detection of malaria parasites in human blood samples. Am J Trop Med Hyg 1999;60:173-6.

Tjitra E, Suprianto S, Dyer M, Currie BJ, Anstey NM. Field evaluation of the ICT malaria P.f/P.v immunochromatographic test for detection of Plasmodium falciparum and Plasmodium vivax in patients with a presumptive clinical diagnosis of malaria in eastern Indonesia. J Clin Microbiol 1999;37:2412-7.

IN REPLY: Dr. Thompson's points are well taken. At the time I wrote my article,¹ I was unaware of the newer multispecies "dipstick" malaria-detection tests he describes.

LYNN W. KITCHEN, M.D., M.P.H.
Professor of Medicine
West Virginia University
Charleston WV 25304-1299

REFERENCE

1. Kitchen LW. Case studies in international travelers. Am Fam Physician 1999;60:471-4.

The True Incidence of GERD-Induced Globus

TO THE EDITOR: The abstract in the recent article¹ on head and neck manifestations of gastroesophageal reflux disease (GERD) contained statistics that did not appear in the body of the article. The authors stated in the abstract that "An estimated 20 to 60 percent of patients with GERD have [ENT] symptoms without a heartburn."¹ The closest data in the body of the article stated that "in 23 to 60 percent of patients presenting with globus sensation, GERD is the etiologic factor."¹ The latter statement gives the incidence of GERD within a specific presenting complaint, whereas the abstract makes a much broader statement regarding the likely presenting symptom among all patients with GERD.

As noted in another article,² inconsistency of data in abstracts is fairly common. However, the accuracy of the abstract is important because this is the section most likely to be read. In this article,¹ the incidence of the presenting complaint in a common disorder is especially important because it is intended to influence how family physicians interpret patient symptoms and formulate differential diagnoses.

Additionally, the authors' assertion (quoted above) that many patients who present with globus sensation have GERD appears flawed. The references that support this assertion come from three subspecialty journal articles, which likely represent a select patient population different from that seen in primary care offices.

The factors discussed above make it difficult to tell if head and neck manifestations of GERD are likely to be an important issue for primary care patients and their physicians.

PETER CARDINAL, M.D.
7211 Beta Drive
Fayetteville, NC 28304-2603

REFERENCES

1. Ahuja V, Yencha MW, Lassen LF. Head and neck manifestations of gastroesophageal reflux disease. Am Fam Physician 1999;60:873-80.

2. Pitkin RM, Branagan MA, Burmeister LF. Accuracy of data in abstracts of published research articles. JAMA 1999;281:1110-1.

IN REPLY: We thank Dr. Cardinal for his comments. The intent of our article¹ was to inform primary care physicians of the atypical (head and neck) presentations of gastroesophageal reflux disease (GERD) and to alert readers that GERD does occur in the absence of the classic "heartburn" symptom. Recognition of patients with this atypical presentation at the primary care level and initiation of treatment is important.

With regard to the abstract percentages, Dr. Cardinal should refer to page 874 of our article.¹ Additionally, because most of the references were from subspecialty journals, the percentages may be slightly biased. For example, in an otolaryngologic practice, the percentage of patients with head and neck symptoms without heartburn approaches 60 percent, while in a primary care setting that number is closer to 20 percent.^2-5 The reason is that patients with heartburn will be diagnosed and treated at the primary care level, avoiding the need for referral. In my practice, the majority of patients referred from primary care physicians and diagnosed with laryngopharyngeal reflux do not report having heartburn; the most common presenting complaint is globus sensation.

Dr. Cardinal's comment on the globus sensation data being flawed is inaccurate. Although the data were obtained from subspecialty journals, the patients in the studies were referred from primary care physicians. Therefore, the data were derived from patients with the complaint of globus sensation who were initially evaluated at the primary care level and then referred for further evaluation. Thus, the patient populations are similar and primary care physicians can expect to evaluate this type of patient complaint.

GERD is a common disorder, and the primary care physician needs to recognize patients with atypical (head and neck) presentations in the absence of heartburn and initiate proper therapy. Early detection and treatment at the primary care level can prevent complications, reduce symptoms, improve quality of life and prevent the need for subspecialty referral.

MYRON W. YENCHA, M.D., F.A.C.S.
Department of Otolaryngology-Head & Neck Surgery
NH-Pensacola
6000 West Highway 98
Pensacola, FL 32512

REFERENCES

1. Vanita A, Yencha MW, Lassen LF. Head and neck manifestations of gastroesophageal reflux disease. Am Fam Physician 1999;60:873-80.

2. Koufman JA. Gastroesophageal reflux and voice disorders. In: Rubin JS, ed. Diagnosis and treatment of voice disorders. New York: Igaku-Shoin, 1995: 161-75.

3. Koufman JA. The otolaryngologic manifestations of gastroesophageal reflux disease (GERD): a clinical investigation of 225 patients using ambulatory 24-hour pH monitoring and an experimental investigation of the role of acid and pepsin in the development of laryngeal injury. Laryngoscope 1991; 101(4 pt 2 suppl 53):1-78.

4. Toohill RJ, Mushtag E, Grossman TW, et al. Pharyngeal, laryngeal, and tracheobronchial manifestations of gastroesophageal reflux. Proceedings of the XXIV World Congress of Otolaryngology-Head and Neck Surgery. Berkeley: Kugler and Ghendini Publishing, 1985.

5. Ossakow SJ, Elta G, Colturi T, Bogdasarian R, Nostrant TT. Esophageal reflux and dysmotility as the basis for persistent cervical symptoms. Ann Otol Rhinol Laryngol 1987;96:387-92.

Corrections

The article "Failure to Pass Meconium: Diagnosing Neonatal Intestinal Obstruction" (November 1, 1999, page 2043) contained an error. Figure 6b on page 2049 was incorrectly cropped.

Question 10 in the March 15, 1999 "Clinical Quiz" (page 1384), pertaining to the article "Vulvodynia and Vulvar Vestibulitis: Challenges in Diagnosis and Management," had two correct choices instead of one. Choices B and C are correct; a history of sexual abuse and limitation of the disease to black women are not characteristic of vulvodynia.

An item in "Quantum Sufficit" (September 1, 1999, page 726), pertaining to health screening in elderly persons, contained a misleading statement. The third sentence of this item should have read: "For example, pneumococcal vaccination should be given once to all elderly persons and revaccination offered after five years to those at highest risk of fatal pneumococcal infection." Current recommendations do not support routine revaccination of elderly patients every five to 10 years.

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