“A robust surveillance system is an essential component of control or elimination programmes”.
VL surveillance and case detection
Several types of data are gathered through surveillance. For VL control, surveillance is primarily focused on patients’ diagnosis and treatment as it is one of the methods to achieve control. Other types of surveillance also exist, with vector surveillance forming a key part of any Leishmania control and elimination programme. In some settings, the monitoring of drug quality and response to treatment (pharmacovigilance) can provide key information on the effectiveness or implementation of programme activities.
Detecting where those infected with VL are is of primary importance for VL control as it enables diagnosis and treatment to be provided promptly (directed to where it is most needed). There are two main forms of surveillance for finding VL cases: passive and active surveillance, which are also known as passive and active case detection (ACD), respectively. These may be used in conjunction with each other. The way to chose among them will depend on the value for money (VfM) of each method together with the overall disease epidemiology and progress of control activties.
Passive case detection occurs when “patients seek care for their illness from clinicians working in static health facilities”. The clinicians who receive and manage a VL case then report accurate information about the case through an appropriate surveillance system to notify a VL case. For the detection of VL, the standard case definition for VL (Step 2.2) is used in combination with the use of an RDT or other diagnostic method.
Though passive case detection is practiced in most L. donovani endemic areas, it does not accurately represent the burden of VL as only a proportion of patients will seek care or be able to access care at a health facility. A variety of factors influence why some VL patients do and some do not seek care. Poor access to care is often related to the high costs of care (if diagnosis/treatment is not free) or transport costs to reach health facilities (if travel costs are not reimbursed) or insecurity due to conflict. Also poor knowledge of the disease results in people seeking care late or not at all. Some patients may report to a health clinic at a very late stage of the disease after visiting alternative, unqualified care providers and some patients, particularly PKDL patients (who do not suffer life –threatening symptoms) may not report at all to a health facility. In certain areas particular social groups may be excluded from accessing health care - perhaps based on gender, age, ethnic background or other.
Active case detection (ACD) occurs when health professionals “reach out to the community and systematically screen the population to find cases of leishmaniasis”. There are different active case finding approaches, which can be employed depending on the situation:
House-to-house search (or blanket screening): health workers visit and screen each member of each house in a community.
Case (or cluster) approach: similar to a house-to-house search, but focused around a reported VL case (or a cluster of cases).
Camp approach: cases with symptoms are gathered in a centralised location for screening. This is used particularly in remote places or to identify new foci of the disease).
Incentive based approach: health workers are given an incentive to get VL cases diagnosed and treated.
Active case detection is highly effective for VL control because it contributes to reducing disease transmission. But it is not always cost effective, especially when endemic areas are very large with a relatively low disease incidence.
Active case detection is mandatory in an elimination program. The earlier the diagnosis and treatment is given, the better the treatment outcomes for patients and the shorter the infectious period of patients.
Active case detection is also more likely to represent the true burden of VL and PKDL - door-to-door active surveillance disproved the view that men were more likely to be affected by PKDL than women in India. Previously, all data on the surveillance of PKDL came from hospital data and relied on self-reporting (passive case detection). It may be that the health care seeking behaviour in the specific area studied had generally been stronger in males. Improving on the treatment-seeking behaviour of patients is an additional crucial area for VL control activities, and information from ACD can thus here help guide those improvements. We will come across the topic of enhancing care access and care seeking behaviour in communities in Steps 4.11 and Step 4.12.
It is, finally, important to note that surveillance can pose serious risks to the participants’ privacy, affect their autonomy and equity and give rise to difficult ethical dilemmas. The WHO has recently published recommendations on how to handle ethical issues in disease surveillance.
© London School of Hygiene and Tropical Medicine 2018