• View in gallery

    Estimated sensitivity of the Newton Nm1 microscope as a function of infection intensity (EPG) as estimated by conventional microscopy. The shaded bars in the histogram depict the distribution of infection intensity in the study population. At an infection intensity > 120 EPG, the sensitivity was 100%.

  • 1.

    Petti CA, Polage CR, Quinn TC, Ronald AR, Sande MA, 2006. Laboratory medicine in Africa: a barrier to effective health care. Clin Infect Dis 42: 377382.

    • Search Google Scholar
    • Export Citation
  • 2.

    Howitt P, Darzi A, Yang G-Z, Ashrafian H, Atun R, Barlow J, Blakemore A, Bull AMJ, Car J, Conteh L, Cooke GS, Ford N, Gregson SAJ, Kerr K, King D, Kulendran M, Malkin RA, Majeed A, Matlin S, Merrifield R, Penfold HA, Reid SD, Smith PC, Stevens MM, Templeton MR, Vincent C, Wilson E, 2012. Technologies for global health. Lancet 380: 507535.

    • Search Google Scholar
    • Export Citation
  • 3.

    Yansouni CP, Bottieau E, Lutumba P, Winkler AS, Lynen L, Büscher P, Jacobs J, Gillet P, Lejon V, Alirol E, Polman K, Utzinger J, Miles MA, Peeling RW, Muyembe JJ, Chappuis F, Boelaert M, 2013. Rapid diagnostic tests for neurological infections in central Africa. Lancet Infect Dis 13: 546558.

    • Search Google Scholar
    • Export Citation
  • 4.

    Utzinger J, Becker SL, van Lieshout L, van Dam GJ, Knopp S, 2015. New diagnostic tools in schistosomiasis. Clin Microbiol Infect 21: 529542.

  • 5.

    Stothard JR, Kabatereine NB, Tukahebwa EM, Kazibwe F, Mathieson W, Webster JP, Fenwick A, 2005. Field evaluation of the Meade Readiview handheld microscope for diagnosis of intestinal schistosomiasis in Ugandan school children. Am J Trop Med Hyg 73: 949955.

    • Search Google Scholar
    • Export Citation
  • 6.

    Bogoch II, Andrews JR, Speich B, Utzinger J, Ame SM, Ali SM, Keiser J, 2013. Mobile phone microscopy for the diagnosis of soil-transmitted helminth infections: a proof-of-concept study. Am J Trop Med Hyg 88: 626629.

    • Search Google Scholar
    • Export Citation
  • 7.

    Bogoch II, Coulibaly JT, Andrews JR, Speich B, Keiser J, Stothard JR, N'Goran EK, Utzinger J, 2014. Evaluation of portable microscopic devices for the diagnosis of Schistosoma and soil-transmitted helminth infection. Parasitology 141: 18111818.

    • Search Google Scholar
    • Export Citation
  • 8.

    Bogoch II, Andrews JR, Speich B, Ame SM, Ali SM, Stothard JR, Utzinger J, Keiser J, 2014. Quantitative evaluation of a handheld light microscope for field diagnosis of soil-transmitted helminth infection. Am J Trop Med Hyg 91: 11381141.

    • Search Google Scholar
    • Export Citation
  • 9.

    Stothard JR, Nabatte B, Sousa-Figueiredo JC, Kabatereine NB, 2014. Towards malaria microscopy at the point-of-contact: an assessment of the diagnostic performance of the Newton Nm1 microscope in Uganda. Parasitology 141: 18191825.

    • Search Google Scholar
    • Export Citation
  • 10.

    Ephraim RKD, Duah E, Cybulski JS, Prakash M, D'Ambrosio MV, Fletcher DA, Keiser J, Andrews JR, Bogoch II, 2015. Diagnosis of Schistosoma haematobium infection with a mobile phone-mounted foldscope and a reversed-lens CellScope in Ghana. Am J Trop Med Hyg 92: 12531256.

    • Search Google Scholar
    • Export Citation
  • 11.

    Keiser J, Utzinger J, 2009. Food-borne trematodiases. Clin Microbiol Rev 22: 466483.

  • 12.

    Sripa B, Bethony JM, Sithithaworn P, Kaewkes S, Mairiang E, Loukas A, Mulvenna J, Laha T, Hotez PJ, Brindley PJ, 2011. Opisthorchiasis and Opisthorchis-associated cholangiocarcinoma in Thailand and Laos. Acta Trop 120 (Suppl 1): S158S168.

    • Search Google Scholar
    • Export Citation
  • 13.

    Fürst T, Sayasone S, Odermatt P, Keiser J, Utzinger J, 2012. Manifestation, diagnosis, and management of foodborne trematodiasis. BMJ 344: e4093.

  • 14.

    Sripa B, Brindley PJ, Mulvenna J, Laha T, Smout MJ, Mairiang E, Bethony JM, Loukas A, 2012. The tumorigenic liver fluke Opisthorchis viverrini—multiple pathways to cancer. Trends Parasitol 28: 395407.

    • Search Google Scholar
    • Export Citation
  • 15.

    Katz N, Chaves A, Pellegrino J, 1972. A simple device for quantitative stool thick-smear technique in schistosomiasis mansoni. Rev Inst Med Trop São Paulo 14: 397400.

    • Search Google Scholar
    • Export Citation
  • 16.

    Speich B, Ali SM, Ame SM, Albonico M, Utzinger J, Keiser J, 2015. Quality control in the diagnosis of Trichuris trichiura and Ascaris lumbricoides using the Kato-Katz technique: experience from three randomised controlled trials. Parasit Vectors 8: 82.

    • Search Google Scholar
    • Export Citation
  • 17.

    Switz NA, D'Ambrosio MV, Fletcher DA, 2014. Low-cost mobile phone microscopy with a reversed mobile phone camera lens. PLoS One 22: e95330.

  • 18.

    Maleewong W, Intapan P, Wongwajana S, Sitthithaworn P, Pipitgool V, Wongkham C, Daenseegaew W, 1992. Prevalence and intensity of Opisthorchis viverrini in rural community near the Mekong River on the Thai-Laos border in northeast Thailand. J Med Assoc Thai 75: 231235.

    • Search Google Scholar
    • Export Citation
  • 19.

    WHO, 1994. Bench Aids for the Diagnosis of Intestinal Parasites. Available at: http://apps.who.int/iris/bitstream/10665/37323/1/9789241544764_eng.pdf. Accessed June 23, 2015.

    • Search Google Scholar
    • Export Citation
  • 20.

    de Vlas SJ, Gryseels B, 1992. Underestimation of Schistosoma mansoni prevalences. Parasitol Today 8: 274277.

  • 21.

    Knopp S, Mgeni AF, Khamis IS, Steinmann P, Stothard JR, Rollinson D, Marti H, Utzinger J, 2008. Diagnosis of soil-transmitted helminths in the era of preventive chemotherapy: effect of multiple stool sampling and use of different diagnostic techniques. PLoS Negl Trop Dis 2: e331.

    • Search Google Scholar
    • Export Citation
  • 22.

    Sayasone S, Utzinger J, Akkhavong K, Odermatt P, 2015. Repeated stool sampling and use of multiple techniques enhance the sensitivity of helminth diagnosis: a cross-sectional survey in southern Lao People's Democratic Republic. Acta Trop 141: 315321.

    • Search Google Scholar
    • Export Citation
  • 23.

    Sithithaworn P, Haswell-Elkins M, 2003. Epidemiology of Opisthorchis viverrini. Acta Trop 88: 187194.

  • 24.

    Sayasone S, Odermatt P, Phoumindr N, Vongsaravane X, Sensombath V, Phetsouvanh R, Choulamany X, Strobel M, 2007. Epidemiology of Opisthorchis viverrini in a rural district of southern Lao PDR. Trans R Soc Trop Med Hyg 101: 4047.

    • Search Google Scholar
    • Export Citation
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

 

 

Diagnosis of Opisthorchis viverrini Infection with Handheld Microscopy in Lao People's Democratic Republic

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  • Divisions of Internal Medicine and Infectious Diseases, University Health Network, Ontario, Canada; Department of Medicine, University of Toronto, Ontario, Canada; National Institute of Public Health, Ministry of Health, Vientiane, Lao People's Democratic Republic; Faculty of Medical Sciences, University of Health Sciences, Vientiane, Lao People's Democratic Republic; Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute and University of Basel, Basel, Switzerland; University of Basel, Basel, Switzerland; Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute and University of Basel, Basel, Switzerland; Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine, Stanford, California

Opisthorchiasis is a neglected tropical disease, yet it is of considerable public health importance in Southeast Asia given the predilection for chronically infected persons to develop cholangiocarcinoma. We evaluated a handheld microscope for the diagnosis of Opisthorchis viverrini in a community-based setting in Lao People's Democratic Republic in comparison with conventional light microscopy. In stool samples collected from 104 individuals, handheld microscopy revealed a sensitivity of 70.6% and a specificity of 89.5% for O. viverrini infection. Pearson's correlation for quantitative fecal egg counts between the two devices was 0.98 (95% confidence interval: 0.98–0.99). With small adjustments to further increase diagnostic sensitivity, a handheld microscope may become a helpful tool to screen for O. viverrini and other helminth infections in public health settings.

Introduction

New diagnostic approaches are necessary to meet the needs of individuals living in resource-constrained settings where access to quality diagnostic testing and other interventions are limited.14 Recently, handheld and mobile phone–based microscopes have been used in public health settings to screen for endemic parasitic diseases, such as malaria, schistosomiasis, and soil-transmitted helminthiasis.510 Such devices may improve access to laboratory diagnoses for clinical and public health practices in resource-constrained settings given their portability and ease of use, thus facilitating point-of-care diagnosis and subsequent patient management.

Opisthorchis viverrini is a liver fluke, common in Southeast Asia, which is acquired by consumption of infected raw or undercooked fish.11 Over 60 million people are at risk of infection and an estimated 9 million are actively infected with O. viverrini, with northern Thailand and central and southern Lao People's Democratic Republic (Lao PDR) heavily affected.12,13 Chronic infection with O. viverrini poses a major public health threat given the predisposition for individuals to develop cholangiocarcinoma, portending a very poor clinical outcome.14

Here we compare the diagnostic accuracy of a handheld microscope to traditional light microscopy for the detection and quantification of O. viverrini infection in an endemic setting of Lao PDR. We discuss the potential usefulness of such devices for mobile public health teams to screen affected populations and for improved patient management at the point of care.

Methods

This study was integrated into a pharmacokinetic and dose-finding study of praziquantel, the current drug of choice against opisthorchiasis. In September 2014, individuals aged 15–65 years who were potentially infected with O. viverrini in three rural communities in southern Lao PDR were screened for enrollment. Ethical approval for this study was granted by the National Ethics Committee for Health Research, Ministry of Health, Lao PDR (reference no. 009/NECHR), and the Ethics Committee of Northern and Central Switzerland (reference no. 2014-162). The trial is registered at Randomized Controlled Trials (identifier: ISRCTN77186750). Participants provided written informed consent.

Before praziquantel administration, we collected three stool samples from each participant on different days within a maximum of 5 days. Stool was processed by the Kato-Katz thick smear technique, with 41.7 mg of stool per slide.15 Slides were examined by senior microscopists via light microscopy using 10×, 20×, and 40× objective lenses on an Olympus CX21 microscope (Olympus, Volketswil, Switzerland). The entire Kato-Katz thick smear was examined for a minimum of 3 min, and the presence or absence of O. viverrini eggs was noted for each individual, and eggs were manually quantified if present. Ten percent of all slides were re-examined by a second expert microscopist blinded to the initial reading to ensure quality control.16

A total of 104 slides from 104 individuals were randomly selected to be re-examined with a Newton Nm1 microscope (Newton Microscopes, Cambridge, United Kingdom) on the same day of stool collection. This is a commercially available, handheld microscope that weighs approximately 480 g and is equipped with modular 10×, 40×, and 100× objective lenses. A senior microscopist, who did not participate in the conventional light microscopy and was blinded to prior results, evaluated slides using this device and recorded the presence or absence of O. viverrini eggs, and quantified eggs in positive samples. A reversed lens mobile phone microscope was also initially used to examine slides; however, there were challenges reliably visualizing eggs with this device and it was not used further in this study.

Data were directly entered into an Excel file (Microsoft, Redmond, WA). We measured the sensitivity and specificity of the Newton microscope using conventional light microscopy considered as the “gold” standard, calculated exact binomial confidence intervals (CIs), and calculated positive predictive values (PPVs) and negative predictive values (NPVs). We modeled the sensitivity of the Newton Nm1 microscope as a function of eggs per gram of stool (EPG) by conventional microscopy using logistic regression. We compared dichotomous agreement using Cohen's κ and quantitative agreement using Pearson's correlation. All analyses were performed using R (R Foundation for Statistical Computing, Vienna, Austria).

Results

Of 104 slides subjected to both diagnostic approaches, conventional microscopy identified O. viverrini eggs in 85 slides (81.7%). Eighty-two slides had low egg counts corresponding to light-intensity infections (1–999 EPG), two slides had moderate egg counts (1,000–9,999 EPG), and one slide demonstrated heavy-intensity infection (> 10,000 EPG).18 The Newton Nm1 microscope was 70.6% (95% CI: 59.6–79.7%) sensitive and 89.5% (95% CI: 65.5–98.2%) specific for O. viverrini diagnosis, with a PPV of 96.8% (95% CI: 87.8–99.4%) and an NPV of 40.5% (95% CI: 26.0–56.7%) (Table 1).

Table 1

Diagnostic operating characteristics of the Newton Nm1 microscope for Opisthorchis viverrini infection in a community-based screening in Lao PDR in September 2014

 Newton Nm1 microscopeTotal
NegativePositive
Conventional microscopyNegative17219
Positive256085
 Total4262104
Sensitivity70.6% (95% CI: 59.6–79.7%) 
Specificity89.5% (95% CI: 65.5–98.2%)
PPV96.8% (95% CI: 87.8–99.4%)
NPV40.5% (95% CI: 26.0–56.7%)

NPV = negative predictive value; PPV = positive predictive value.

As the intensity of infection increased, so did diagnostic sensitivity, with sensitivity exceeding 90% at 75 EPG and reaching 100% at > 120 EPG (Figure 1). Comparing conventional light microscopy to the Newton Nm1 microscope for O. viverrini diagnosis, Cohen's κ was 0.41 (95% CI: 0.41–0.57), indicating moderate agreement. We found a very high Pearson's correlation of 0.98 (95% CI: 0.98–0.99).

Figure 1.
Figure 1.

Estimated sensitivity of the Newton Nm1 microscope as a function of infection intensity (EPG) as estimated by conventional microscopy. The shaded bars in the histogram depict the distribution of infection intensity in the study population. At an infection intensity > 120 EPG, the sensitivity was 100%.

Citation: The American Society of Tropical Medicine and Hygiene 94, 1; 10.4269/ajtmh.15-0525

Discussion

New pragmatic strategies are required to diagnose neglected tropical diseases given the lack of readily available tools in most endemic countries. Portable and mobile phone microscopy may be a practical solution to many of the current barriers to quality diagnostic testing in rural, remote, and resource-constrained settings. Herein, we show that the Newton Nm1 field microscope has moderate sensitivity and very good specificity for the diagnosis of O. viverrini infection within the frame of a community-based screening approach in a highly endemic area of Lao PDR.

The moderate sensitivity of the Newton Nm1 microscope may be due to a variety of reasons. First, O. viverrini eggs are quite small and translucent.19 Hence, given the high proportion of light-intensity infections in this setting (82 of the 85 O. viverrini-positive individuals had fewer than 1,000 EPG, which translates to < 42 eggs per slide), microscopists may have simply not visualized eggs while scanning over the Kato-Katz thick smears with this device. Second, as the device is handheld, microscopists may miscount eggs due to motion artifact. We feel that the device is best used with a small tripod attached to ensure image stability and prevent user's fatigue when examining slides. In addition, the stage of the Newton Nm1 microscope is designed to secure and maneuver a microscope slide in the x and y axes as per conventional microscopes. Because of the Newton Nm1's compact design, the extent of slide motion is limited compared with conventional light microscopes, and if a Kato-Katz thick smear is spread out over a wide area on a slide, the edges of that thick smear may not be visualized with the Newton Nm1 device. This issue was first noted during a field study evaluating handheld microscopes for the diagnosis of Schistosoma mansoni and Schistosoma haematobium in Côte d'Ivoire, where, on average, fewer eggs were counted on slides examined with portable microscopes compared with conventional microscopes.7 Subsequent quantification and analytic studies demonstrated excellent correlation and concordance between the Newton Nm1 microscope and conventional light microscopy when egg counts were multiplied by a “correction factor.”8

Potential solutions to mitigate the Newton Nm1 microscope's decreased sensitivity include ensuring that the specimen is placed on the center of the slide and that the sample is not spread over too wide an area. This simple adjustment will ensure that the microscopist can visualize the entire sample. Other approaches to increase diagnostic sensitivity include examining multiple slides as the Kato-Katz technique may have false-negative readings while examining slides with low infection intensity.2022 Because of the high prevalence of O. viverrini infection and moderate sensitivity of this device, the NPV was somewhat poor, and hence this device was not reliable in ruling out infections. In addition, the prevalence of infection was higher in this study compared with prior field studies.23,24 We would expect the PPV of the Newton portable microscope to decline in settings with lower O. viverrini prevalence, and the NPV to increase in such settings. However, the device demonstrated excellent sensitivity at higher egg intensities (particularly at 120 EPG, which are still categorized as light-intensity infections) and had good quantitative correlation with conventional microscopy; both of these attributes make it potentially useful for epidemiologic surveys in remote settings. Since only an expert microscopist used the Newton Nm1 microscope, future studies should also evaluate the use of this device by frontline health-care personnel, such as laboratory technicians.

The Newton Nm1 microscope requires three AAA batteries and can provide over 200 hours of continuous use. A differential price structure exists to allow for greater affordability and use in low-income countries. As the Newton Nm1 microscope functions like a miniaturized version of a conventional light microscope, slides must still be prepared as per routine laboratory protocols prior to viewing. The advantages of this device include its light weight (480 g), ease of use, portability, and that sample preparation for many neglected tropical diseases (e.g., intestinal and biliary parasitoses) and malaria can be easily performed in field settings, making this device a potentially helpful diagnostic tool outside conventional laboratories.

In conclusion, handheld light microscopy shows promise as a valuable public health tool for the detection and quantification of neglected tropical infections, such as O. viverrini in community-based settings. The role of these handheld devises for improved case management at the point of care warrants follow-up studies.

  • 1.

    Petti CA, Polage CR, Quinn TC, Ronald AR, Sande MA, 2006. Laboratory medicine in Africa: a barrier to effective health care. Clin Infect Dis 42: 377382.

    • Search Google Scholar
    • Export Citation
  • 2.

    Howitt P, Darzi A, Yang G-Z, Ashrafian H, Atun R, Barlow J, Blakemore A, Bull AMJ, Car J, Conteh L, Cooke GS, Ford N, Gregson SAJ, Kerr K, King D, Kulendran M, Malkin RA, Majeed A, Matlin S, Merrifield R, Penfold HA, Reid SD, Smith PC, Stevens MM, Templeton MR, Vincent C, Wilson E, 2012. Technologies for global health. Lancet 380: 507535.

    • Search Google Scholar
    • Export Citation
  • 3.

    Yansouni CP, Bottieau E, Lutumba P, Winkler AS, Lynen L, Büscher P, Jacobs J, Gillet P, Lejon V, Alirol E, Polman K, Utzinger J, Miles MA, Peeling RW, Muyembe JJ, Chappuis F, Boelaert M, 2013. Rapid diagnostic tests for neurological infections in central Africa. Lancet Infect Dis 13: 546558.

    • Search Google Scholar
    • Export Citation
  • 4.

    Utzinger J, Becker SL, van Lieshout L, van Dam GJ, Knopp S, 2015. New diagnostic tools in schistosomiasis. Clin Microbiol Infect 21: 529542.

  • 5.

    Stothard JR, Kabatereine NB, Tukahebwa EM, Kazibwe F, Mathieson W, Webster JP, Fenwick A, 2005. Field evaluation of the Meade Readiview handheld microscope for diagnosis of intestinal schistosomiasis in Ugandan school children. Am J Trop Med Hyg 73: 949955.

    • Search Google Scholar
    • Export Citation
  • 6.

    Bogoch II, Andrews JR, Speich B, Utzinger J, Ame SM, Ali SM, Keiser J, 2013. Mobile phone microscopy for the diagnosis of soil-transmitted helminth infections: a proof-of-concept study. Am J Trop Med Hyg 88: 626629.

    • Search Google Scholar
    • Export Citation
  • 7.

    Bogoch II, Coulibaly JT, Andrews JR, Speich B, Keiser J, Stothard JR, N'Goran EK, Utzinger J, 2014. Evaluation of portable microscopic devices for the diagnosis of Schistosoma and soil-transmitted helminth infection. Parasitology 141: 18111818.

    • Search Google Scholar
    • Export Citation
  • 8.

    Bogoch II, Andrews JR, Speich B, Ame SM, Ali SM, Stothard JR, Utzinger J, Keiser J, 2014. Quantitative evaluation of a handheld light microscope for field diagnosis of soil-transmitted helminth infection. Am J Trop Med Hyg 91: 11381141.

    • Search Google Scholar
    • Export Citation
  • 9.

    Stothard JR, Nabatte B, Sousa-Figueiredo JC, Kabatereine NB, 2014. Towards malaria microscopy at the point-of-contact: an assessment of the diagnostic performance of the Newton Nm1 microscope in Uganda. Parasitology 141: 18191825.

    • Search Google Scholar
    • Export Citation
  • 10.

    Ephraim RKD, Duah E, Cybulski JS, Prakash M, D'Ambrosio MV, Fletcher DA, Keiser J, Andrews JR, Bogoch II, 2015. Diagnosis of Schistosoma haematobium infection with a mobile phone-mounted foldscope and a reversed-lens CellScope in Ghana. Am J Trop Med Hyg 92: 12531256.

    • Search Google Scholar
    • Export Citation
  • 11.

    Keiser J, Utzinger J, 2009. Food-borne trematodiases. Clin Microbiol Rev 22: 466483.

  • 12.

    Sripa B, Bethony JM, Sithithaworn P, Kaewkes S, Mairiang E, Loukas A, Mulvenna J, Laha T, Hotez PJ, Brindley PJ, 2011. Opisthorchiasis and Opisthorchis-associated cholangiocarcinoma in Thailand and Laos. Acta Trop 120 (Suppl 1): S158S168.

    • Search Google Scholar
    • Export Citation
  • 13.

    Fürst T, Sayasone S, Odermatt P, Keiser J, Utzinger J, 2012. Manifestation, diagnosis, and management of foodborne trematodiasis. BMJ 344: e4093.

  • 14.

    Sripa B, Brindley PJ, Mulvenna J, Laha T, Smout MJ, Mairiang E, Bethony JM, Loukas A, 2012. The tumorigenic liver fluke Opisthorchis viverrini—multiple pathways to cancer. Trends Parasitol 28: 395407.

    • Search Google Scholar
    • Export Citation
  • 15.

    Katz N, Chaves A, Pellegrino J, 1972. A simple device for quantitative stool thick-smear technique in schistosomiasis mansoni. Rev Inst Med Trop São Paulo 14: 397400.

    • Search Google Scholar
    • Export Citation
  • 16.

    Speich B, Ali SM, Ame SM, Albonico M, Utzinger J, Keiser J, 2015. Quality control in the diagnosis of Trichuris trichiura and Ascaris lumbricoides using the Kato-Katz technique: experience from three randomised controlled trials. Parasit Vectors 8: 82.

    • Search Google Scholar
    • Export Citation
  • 17.

    Switz NA, D'Ambrosio MV, Fletcher DA, 2014. Low-cost mobile phone microscopy with a reversed mobile phone camera lens. PLoS One 22: e95330.

  • 18.

    Maleewong W, Intapan P, Wongwajana S, Sitthithaworn P, Pipitgool V, Wongkham C, Daenseegaew W, 1992. Prevalence and intensity of Opisthorchis viverrini in rural community near the Mekong River on the Thai-Laos border in northeast Thailand. J Med Assoc Thai 75: 231235.

    • Search Google Scholar
    • Export Citation
  • 19.

    WHO, 1994. Bench Aids for the Diagnosis of Intestinal Parasites. Available at: http://apps.who.int/iris/bitstream/10665/37323/1/9789241544764_eng.pdf. Accessed June 23, 2015.

    • Search Google Scholar
    • Export Citation
  • 20.

    de Vlas SJ, Gryseels B, 1992. Underestimation of Schistosoma mansoni prevalences. Parasitol Today 8: 274277.

  • 21.

    Knopp S, Mgeni AF, Khamis IS, Steinmann P, Stothard JR, Rollinson D, Marti H, Utzinger J, 2008. Diagnosis of soil-transmitted helminths in the era of preventive chemotherapy: effect of multiple stool sampling and use of different diagnostic techniques. PLoS Negl Trop Dis 2: e331.

    • Search Google Scholar
    • Export Citation
  • 22.

    Sayasone S, Utzinger J, Akkhavong K, Odermatt P, 2015. Repeated stool sampling and use of multiple techniques enhance the sensitivity of helminth diagnosis: a cross-sectional survey in southern Lao People's Democratic Republic. Acta Trop 141: 315321.

    • Search Google Scholar
    • Export Citation
  • 23.

    Sithithaworn P, Haswell-Elkins M, 2003. Epidemiology of Opisthorchis viverrini. Acta Trop 88: 187194.

  • 24.

    Sayasone S, Odermatt P, Phoumindr N, Vongsaravane X, Sensombath V, Phetsouvanh R, Choulamany X, Strobel M, 2007. Epidemiology of Opisthorchis viverrini in a rural district of southern Lao PDR. Trans R Soc Trop Med Hyg 101: 4047.

    • Search Google Scholar
    • Export Citation

Author Notes

* Address correspondence to Isaac I. Bogoch, Divisions of Internal Medicine and Infectious Diseases, Toronto General Hospital, 14EN-209, 200 Elizabeth Street, Toronto, Ontario, Canada M5G 2C4. E-mail: isaac.bogoch@uhn.ca† These authors contributed equally to this work.

Financial support: Isaac I. Bogoch is supported by a grant from Grand Challenges Canada. Jennifer Keiser is grateful to the Swiss National Science Foundation (no. 320030_14930/1) for financial support.

Authors' addresses: Isaac I. Bogoch, Division of Internal Medicine and Infectious Diseases, Toronto General Hospital, Ontario, Canada, E-mail: isaac.bogoch@uhn.ca. Somphou Sayasone, National Institute of Public Health, Ministry of Health, Vientiane, Lao People's Democratic Republic, E-mail: somphou.sayasone@yahoo.com. Youthanavanh Vonghachack, Faculty of Medical Sciences, University of Health Sciences, Vientiane, Lao People's Democratic Republic, E-mail: youthanavanh.vonghachack@yahoo.com. Isabel Meister and Jennifer Keiser, Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute and University of Basel, Basel, Switzerland, E-mails: isabel.meister@unibas.ch and jennifer.keiser@unibas.ch. Jürg Utzinger and Peter Odermatt, Department of Epidemiology and Public Health, Swiss Tropical Institute and University of Basel, Basel, Switzerland, E-mails: juerg.utzinger@unibas.ch and peter.odermatt@unibas.ch. Jason R. Andrews, Division of Infectious Diseases and Geographic Medicine, Stanford University, Stanford, CA, E-mail: jandr@stanford.edu.

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