Integrating Facility-Based Surveillance With Healthcare Utilization Surveys to Estimate Enteric Fever Incidence: Methods and Challenges

Abstract

Cohort studies and facility-based sentinel surveillance are common approaches to characterizing infectious disease burden, but present trade-offs; cohort studies are resource-intensive and may alter disease natural history, while sentinel surveillance underestimates incidence in the population. Hybrid surveillance, whereby facility-based surveillance is paired with a community-based healthcare utilization assessment, represents an alternative approach to generating population-based disease incidence estimates with moderate resource investments. Here, we discuss this method in the context of the Surveillance for Enteric Fever in Asia Project (SEAP) study. We describe how data are collected and utilized to adjust enteric fever incidence for blood culture sensitivity, facility-based enrollment, and healthcare seeking, incorporating uncertainty in these parameters in the uncertainty around incidence estimates. We illustrate how selection of surveillance sites and their coverage may influence precision and bias, and we identify approaches in the study design and analysis to minimize and control for these biases. Rigorously designed hybrid surveillance systems can be an efficient approach to generating population-based incidence estimates for infectious diseases.

Under-detection of blood culture-positive enteric fever cases: The impact of missing data and methods for adjusting incidence estimates

“…Crude typhoid incidence estimates can be adjusted for various factors that affect the underdetection of cases. [4] As a minimum, crude incidence estimates are often adjusted for the poor sensitivity of blood culture tests; [5] among those with typhoid fever, only around 60% of individuals who receive a blood culture are expected to test positive. [3] Additionally, incidence can be adjusted to account for missed cases using inflation factors based on data from community surveys or other sources of information on health-care seeking behaviour.…”

Estimation of Incidence of Typhoid and Paratyphoid Fever in Vientiane, Lao People’s Democratic Republic

“…8 Over the past two decades, hybrid surveillance methods, also known as "multiplier studies," combining sentinel surveillance with healthcare utilization surveys to adjust for under-ascertainment have been developed and applied to provide a practical means of estimating infectious disease incidence. 8,9 In 2017, the WHO Strategic Advisory Group of Experts on immunization recommended a routine use of typhoid conjugate vaccine in infants and children aged > 6 months in typhoid-endemic countries. 10 National decisions about typhoid conjugate vaccine introduction can be informed by robust typhoid incidence data.…”

Phase I of the Surveillance for Enteric Fever in Asia Project (SEAP): An Overview and Lessons Learned

“…Unlike Phase I, Phase II will be able to estimate incidence on the basis of data from hospital-based surveillance, using the low-cost hybrid method outlined by Luby et al [ 17 ]. We plan to obtain the proportion of participants with disease matching our case definition who sought healthcare and create age-stratified incidence by using healthcare-seeking behavior, as well as to adjust for a variety of factors related to potential biases as described by another article in this supplement [ 22 ], to deliver more-discrete and accurate estimates to country governments and decision makers.…”