The role of supplementary environmental surveillance to complement acute flaccid paralysis surveillance for wild poliovirus in Pakistan and Afghanistan - January 2011 through September 2013 Open Access

Cowger, Victoria Lauren (2014)

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Introduction. Since 1988, poliomyelitis incidence has decreased more than 99% worldwide. The current gold-standard for poliovirus surveillance is clinical Acute Flaccid Paralysis (AFP) surveillance; however, there is evidence of decreased sensitivity of AFP surveillance with decreasing infection prevalence. Environmental surveillance (ENV) can detect circulating polioviruses from sewage excreted in stool without relying on clinical presentation of disease, making it a potentially powerful complement to AFP surveillance. Because of the extensive ENV and continued endemicity, Pakistan presents a unique opportunity to quantify the role of ENV as a supplement to AFP surveillance alone. Methods. Teams at the U.S. Centers for Disease Control and Prevention (CDC) provided genetic, geographic and temporal data for Pakistan and Afghanistan poliovirus isolates from January 2011 through September 2013. Descriptive analysis was conducted to quantify WPV positive isolates by surveillance type, year and country. AFP and ENV isolates were mapped by year, location, and genetic cluster to compare genetic distribution of isolates detected by respective surveillance types. Pakistan AFP isolates were classified into sub-lineages based genetic match to other Pakistan AFP isolates and similar genetic circulation preceding and following sub-lineage isolates were plotted and circulation time for both ENV and AFP surveillance was quantified. Results. A total of 803 WPV isolates were detected by AFP and ENV surveillance in Pakistan and Afghanistan from January 2011 through September 2013. In six of the first seven months of 2011, ENV detected poliovirus in samples in three provinces that did not detect any polio cases, suggesting silent transmission in these areas. Overall, ENV detected circulation first in more sub-lineages than did AFP (51.7% vs. 26.3%), and ENV detected circulation approximately 2 months sooner on average for each sub-lineage than did AFP surveillance. Discussion. This study presents evidence that suggests ENV in Pakistan is providing earlier and more sensitive detection than AFP surveillance alone. Overall, targeted ENV through strategic selection of sites has proven useful in Pakistan, and has important applications in the eradication Endgame strategy, including detecting cVDPVs, monitoring the switch from live to inactivated polio vaccine, and certification of a polio-free world.

Table of Contents


Overview of Polio and poliovirus.
Clinical features
Polio vaccines
Polio epidemiology and eradication

Surveillance for Polio
Acute Flaccid Paralysis surveillance
Environmental Surveillance

Epidemiology and Environmental surveillance for poliovirus in Pakistan
Genetic classification
Descriptive analysis
Orphan lineage analysis
Sub-lineage analysis
Descriptive analysis
Orphan lineage analysis
Sub-lineage analysis
Detection above AFP surveillance alone
Strengths and weaknesses of analyses

Limitations and considerations for implementation of ENV
Role of environmental surveillance in endgame strategy


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