RESUMO
Response to and monitoring of viral outbreaks can be efficiently focused when rapid, quantitative, kinetic information provides the location and the number of infected individuals. Environmental surveillance traditionally provides information on location of populations with contagious, infected individuals since infectious poliovirus is excreted whether infections are asymptomatic or symptomatic. Here, we describe development of rapid (1 week turnaround time, TAT), quantitative RT-PCR of poliovirus RNA extracted directly from concentrated environmental surveillance samples to infer the number of infected individuals excreting poliovirus. The quantitation method was validated using data from vaccination with bivalent oral polio vaccine (bOPV). The method was then applied to infer the weekly number of excreters in a large, sustained, asymptomatic outbreak of wild type 1 poliovirus in Israel (2013) in a population where >90% of the individuals received three doses of inactivated polio vaccine (IPV). Evidence-based intervention strategies were based on the short TAT for direct quantitative detection. Furthermore, a TAT shorter than the duration of poliovirus excretion allowed resampling of infected individuals. Finally, the method documented absence of infections after successful intervention of the asymptomatic outbreak. The methodologies described here can be applied to outbreaks of other excreted viruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), where there are (1) significant numbers of asymptomatic infections; (2) long incubation times during which infectious virus is excreted; and (3) limited resources, facilities, and manpower that restrict the number of individuals who can be tested and re-tested.
RESUMO
Environmental surveillance (EnvS)2 is an important tool for monitoring the presence of poliovirus in endemic and poliovirus free regions. Unlike acute flaccid paralysis (AFP)3 surveillance, EnvS can monitor large populations using small numbers of samples and detect the introduction of poliovirus even before the appearance of AFP cases. Early detection and timely response can prevent the onset of poliovirus associated AFP, as was demonstrated by silent poliovirus transmission in Israel in 2013. Although EnvS is currently recommended as supplementary to AFP surveillance, it is limited to laboratories with equipment for poliovirus concentration and to regions where samples can be easily transported under temperature controlled conditions to such facilities. However the highest risk of poliovirus re-emergence is in developing countries where such conditions do not exist. We developed and evaluated an affinity purification method using antibody or poliovirus receptor (CD155) presenting bacteriophage covered magnetic beads for poliovirus concentration. This method requires only simple, inexpensive and portable equipment. Though tested only on Sabin 1 spiked sewage samples it provided better recovery than our current polyethylene glycol (PEG)4/NaCl- based concentration method. On site use of this method might facilitate EnvS in currently inaccessible remote regions by significantly reducing the volume of sample that needs to be transported back to the laboratory under temperature-controlled conditions5.
