Conference abstract

Sensitivity and positive predictive value of the measles surveillance system in Uganda, 2012-2015

Pan African Medical Journal - Conference Proceedings. 2017:6(20).21 Dec 2017.
doi: 10.11604/pamj-cp.2017.6.20.503

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Keywords: Measles, surveillance system, Uganda
Plenary

Sensitivity and positive predictive value of the measles surveillance system in Uganda, 2012-2015

Fred Nsubuga1,&, Immaculate Ampaire2, Alex Riolexus Ario1, Henry Luzze2, Simon Kasasa3

1Uganda Public Health Fellowship Program, Kampala, Uganda, 2Ministry of Health, Kampala, Uganda, 3Makerere University School of Public Health, Kampala, Uganda

&Corresponding author
Fred Nsubuga, Uganda Public Health Fellowship Program, Kampala, Uganda

Abstract

Introduction: disease surveillance is a critical component in the control and elimination of vaccine preventable diseases. The Uganda National Expanded Program on Immunization strives to have a sensitive surveillance system within the Integrated Disease Surveillance and Response (IDSR) framework. We analyzed measles surveillance data to determine the effectiveness of the measles case-based surveillance system and estimate its positive predictive value in order to inform policy and practice.

Methods: an IDSR alert was defined as 1 suspected measles case reported by a district in a week, through the electronic Health Management Information System. We defined an alert in the measles case-based surveillance system (CBS) as 1 suspected measles case with a blood sample collected for confirmation during the corresponding week in a particular district. Effectiveness of CBS was defined as having 80% of IDSR alerts with a blood sample collected for laboratory confirmation. Positive predictive value was defined as the proportion of measles case-patients who also had a positive measles serological result (IgM +). We reviewed case-based surveillance data with laboratory confirmation and measles surveillance data from the electronic Health Management Information System from 2012-2015.

Results: a total of 6,974 suspected measles case-persons were investigated by the measles case-based surveillance between 2012 and 2015. Of these, 943 (14%) were measles specific IgM positive. The median age of measles case-persons between 2013 and 2015 was 4.0 years. Between 2013 and 2015, 72% of the IDSR alerts reported in the electronic Health Management Information System, had blood samples collected for laboratory confirmation. This was however less than the WHO recommended standard of 80%. The PPV of CBS between 2013 and 2015 was 8.6%.

Conclusion: effectiveness of measles case-based surveillance was sub-optimal, while the PPV showed that true measles cases have significantly reduced in Uganda. We recommended strengthening of case-based surveillance to ensure that all suspected measles cases have blood samples collected for laboratory confirmation to improve detection and ensure elimination by 2020.