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. Author manuscript; available in PMC: 2016 Apr 27.
Published in final edited form as: Adv Parasitol. 2014;84:151–208. doi: 10.1016/B978-0-12-800099-1.00003-X

Table 1.

Summary of sampling issues, accuracy and precision of major malaria transmission metrics

Sampling issues Accuracy Precision
Net infectiousness of humans to mosquitoes (κ)

  • Feeding assays: restriction to patent gametocyte carriers leads to different answers than xenodiagnostic studies

  • Wild-caught vector infection rates: Sampling mosquitoes will affected by natural variations in mosquito populations

  • Poor association with transmission intensity

  • Mosquito feeding assays need to take into account the likelihood of being bitten

  • Skin feeding assays may result in higher infection rates than membrane feeding assays1

  • Susceptibility of mosquito colony may differ from wild-caught mosquitoes

  • Affected by seasonality, natural variation in mosquito populations and frequency of sampling

  • Mosquito feeding assays have unknown precision
Parasite rate in humans (PR)

  • Age groups for sampling affect estimates

  • Seasonal patterns affect outcomes

  • Convenience sampling leads to selection bias with plausibly more parasite-positive individuals (cluster sampling approach)

  • Substantial proportion of infections will be missed by microscopy and RDTs

  • PR depends on season and age-groups.

  • Standardized sampling approach in combination with high quality microscopy methodology will allow good precision

  • Consistency in methodology is required
Entomological inoculation rate (EIR)

  • Seasonal variation

  • Convenience sampling (selecting high burden households) may bias estimates

  • Relative contribution of outdoor biting to transmission poorly characterised

  • Variation in procedures to sample mosquitoes

  • Inconsistencies in protocols for the same procedures

  • Heterogeneous biting limits accuracy at high transmission intensity

  • Ma difficult to measure precisely due to spatial, temporal and seasonal variability in vector density

  • SR affected by initial infectiousness and average age of adult mosquitoes
Force of infection (FOI), molecular force of infection (mFOI) and

  • Age groups for sampling affect estimates

  • Seasonal patterns affect outcomes

  • Convenience sampling leads to selection bias with plausibly more parasite-positive individuals (cluster sampling approach)

  • FOI, but probably not mFOI will saturate at a certain transmission intensity

  • Strong association between mFOI and seasonality, age and ITN use indicates relatively high accuracy

  • Variation in sample quality and extraction efficiency may result in fluctuations between surveys2

  • Fluctuation in parasite densities below detection thresholds limits precision
Multiplicity of infection (MOI)

  • Age groups for sampling affect estimates

  • Seasonal patterns affect outcomes

  • Convenience sampling leads to selection bias with plausibly more parasite-positive individuals (cluster sampling approach)

  • Substantial number of clones may be missed by PCR if sampling is restricted to one day3

  • Accuracy limited by diversity of parasite clones

  • Variation in sample quality/extraction efficiency that may result in fluctuations between surveys2
Seroconversion rate (SCR)

  • Age groups for sampling affect estimates

  • Seasonal patterns affect outcomes

  • Convenience sampling leads to selection bias with plausibly more parasite-positive individuals (cluster sampling approach)

  • Short-lived and long-lived responses will affect accuracy

  • Limitations in detecting small changes in transmission intensity

  • Standardized procedures and positive controls make precision of estimates reasonably high
Clinical surveillance: slide positivity rate (SPR), incidence of clinical malaria and proportion of fevers with P. falciparum parasitaemia (PFPf)

  • Attendance to health facilities varies

  • Clinical decision making4

  • Clinic attendance to health facilities may be suboptimal and vary between times and sites

  • Saturation of incidence at high transmission intensities

  • SPR and PFPf affected by incidence of other febrile illness

  • Depends on consistency in diagnostic practices and methodology
Vectorial capacity (C) and the basic reproduction number (R0)

  • C and R0 difficult to measure directly

  • Convenience entomological sampling (selecting high burden households) may bias estimates of C

  • C and R0 only as accurate as their constituent components.

  • Relative contribution of outdoor biting to transmission poorly characterised

  • Variation in procedures to sample mosquitoes

  • Precision affected by natural fluctuations in vector densities, biting patterns and variation in performance of trapping methods

  • When measuring R0, heterogeneous biting must be accounted for
1

Bousema, T., et al., 2012. Mosquito feeding assays to determine the infectiousness of naturally infected Plasmodium falciparum gametocyte carriers. PLoS One, 7, e42821;

2

Baidjoe, A., et al., In press. Combined DNA extraction and antibody elution from filter papers for the assessment of malaria transmission intensity in epidemiological studies. Malar J;

3

Koepfli, C., et al., 2011. How much remains undetected? Probability of molecular detection of human Plasmodia in the field. PLoS One 6, e19010;

4

Bastiens, G., et al., 2011. Malaria diagnostic testing and treatment practices in three different Plasmodium falciparum transmission settings in Tanzania: before and after a government policy change. Malar J. 10, 76.