CONTRIBUTO AL PROGETTO OMS DI ERADICAZIONE DELLA POLIOMIELITE: RISULTATI DELLE ATTIVITÀ DI SORVEGLIANZA IN LOMBARDIA.

A contribution to the WHO global polio eradication initiative: the results of surveillance activities in Lombardy (Northern Italy), 2012-2015. Although in 2015 poliovirus (PV) transmission has been reported at the lowest levels ever recorded, the virus is still endemic in two countries – Afghanistan and Pakistan. Until PV transmission is interrupted in these countries, all countries remain at risk of virus importation - especially vulnerable countries with weak public health and immunization services and travel or trade links to endemic countries. The high levels of immigration flows across the Mediterranean Sea jeopardize Italy for PV reintroduction. The “WHO Strategic Plan of the Global Polio Eradication Initiative” indicates the nationwide surveillance of Acute Flaccid Paralysis (AFP) as the gold standard for detecting cases of poliomyelitis. In addition, systematic Environmental Surveillance (ES), seeking the presence of PV in sewage, is recognized as a powerful tool to confirm PV circulation in absence of AFP cases, especially in polio-free countries. In Italy, nationwide AFP surveillance has been set up in 1997, and ES has been established since 2005 in Milan and other five Italian cities (Bolzano, Parma, Sassari, Napoli and Palermo). This PhD project aimed at evaluating these two public health surveillance systems ongoing in Lombardy (Northern Italy) in the period spanning from 2012 to 2015, in order to improve their quality and efficiency, and to achieve the WHO criteria. The results of surveillance activities were described and the assessment of system attributes (including data quality, sensitivity and timeliness) were discussed. Additionally, in the framework of the ES, the circulation and characterization of non-polio Enterovirus (NPEV) was evaluated in the study population. The surveillance activities were carried out according to WHO guidelines from January 2012 to October 2015. For AFP surveillance, all children <15 years who met the WHO definition of AFP case were enrolled, and the collection of stool and serum samples from each case was requested. For ES, wastewater samples were collected twice a month at the intel of 3 wastewater treatment plants located in Milan. Stool specimens collected from AFP cases and wastewater samples were analyzed to detect PV and NPEVs by virus isolation in RD (human rhabdomyosarcoma) and L20B (murine transgenic L cells) cell cultures, and by PCR assay specific for the 5′ noncoding region [5′NCR] (nucleotide [nt]: 179-575). The identified viruses were genotyped by sequence analysis of the VP1 gene (nt. 2602-2977). In order to define the serological status/immunity against PV, serum samples collected from AFP cases were analyzed by microneutralization assay against PV1, PV2, and PV3. According to WHO, an antibody titre >1:8 was considered protective. From January 2012 to October 2015, 52 AFP cases were reported in Lombardy with an incidence rate of 1.04/100’000 children <15 years of age. The median age of AFP cases was 5.8 years [inter-quartile range (IQR): 10.0 years]; no gender difference was observed. The annual incidence rates were 0.8/100’000 in 2012, 1.5/100’000 in 2013, 1.1/100’000 in 2014, and 0.6/100’000 in 2015 (preliminary data up to October). According to the WHO, the sensitivity of the AFP surveillance system is considered adequate when at least one case of AFP is detected annually per 100’000 children aged less than 15 years. As in 2012 the sensitivity of the surveillance system did not met this criterion, several interventions were implemented to raise awareness among the parts involved in the surveillance. On purpose, reports on the AFP notified weekly by sentinel hospitals were sent out quarterly to all physicians involved in the surveillance system along with epidemiological alerts and bulletins on PV circulation and polio endgame. Phone and e-mail contacts were kept with physicians who reported AFP cases to guarantee the adequacy of notification. Moreover, a workshop on PV and its surveillance system was arranged in collaboration with regional and national (ISS) public health authorities. These actions allowed the sensitivity of the AFP surveillance system to meet the WHO criterion from 2013 onwards. The WHO recommends completing the case investigation by virological analysis of stool samples in at least 80% of AFP cases: during our study, this rate was achieved in 2014 and 2015 (85.7%), whereas in 2012 and 2013 the analysis was completed in 63.6% and 60% of stool samples, respectively. The improvement of virological investigation completeness of AFP cases since 2014 was probably due to the raised awareness of physicians involved in the surveillance. About 40% (21/52) of AFP cases were diagnosed as Guillain-Barré syndrome, 23.1% (12/52) and 19.2% (10/52) were ascribed to genetic disease and myelitis, respectively. Most (35/52; 67%) of AFP cases were reported by pediatric wards during summer and winter. According to virological results, no AFP case was caused by a PV infection, even though one AFP case (that occurred in 2014 in a 6-month boy affected by Bruton disease who received the first dose of oral polio vaccine in Albania) was characterized as a vaccine associated paralytic paralysis (VAPP). NPEVs were detected in 6 AFP cases (10.5%): 2 were Echovirus-11, 1 was Echovirus-6, and the remaining 3 were not genotyped. Serological investigation was carried out in 48 (48/52: 92.3%) AFP cases and a protective antibody titre (neutralising antibodies titre ≥1:8) was detected in 94% (45/48) of individuals. In the framework of the ES, 273 wastewater samples were collected and no PVs were isolated. In contrast, NPEVs were detected in 65.2% (172/273) of tested samples. The proportion of NPEVs detected in sewage by year was 70% (42/60) in 2012, 56.9% (41/72) in 2013, 66.7% (48/72) in 2014 and 68.3% (41/60) in 2015 (up to October). In 2013 the rate of NPEVs detected was significantly lower (p< .05) than those recorded in the other years of study. The WHO declares that at least 30% of samples collected in the ES setting have to be positive for NPEV, thus our results demonstrated the good performance of the ongoing surveillance system in the whole study period. All NPEVs were characterized as EV belonging to species B: Echovirus-11 and Echovirus-6 were the most frequently detected viruses, being the 29.1% (41/141) and 20.6% (29/141) of genotyped NPEVs, respectively. No difference among the NPEV genotypes circulating in the three wastewater treatment plants was identified. It is important to strengthen surveillance of AFP cases at regional and national level in order to detect rapidly any virus importation or emergence and enable a prompt public health response. Although AFP surveillance remains the gold standard, systematic ES is a powerful tool to detect PV in the absence of polio cases, especially in polio-free countries. During our study, AFP surveillance met the WHO criteria for sensitivity from 2013 onwards and the level of completeness of case investigation improved significantly from 2014. Physicians involved in the activities have proved to give special attention to AFP surveillance thanks to several initiatives implemented since 2013, such as the sharing of surveillance reports, epidemiological alerts and updates on polio eradication progress. Epidemiological features of AFP cases were similar to those reported in the current scientific literature and our data confirm adequate levels of immunization in population as well as the absence of wild PV infections. ES was suitable to investigate EV circulation in the population and the high rate of NPEV detected underlines a massive virus circulation. No silent PV reintroduction was noted during ES. As long as in the current polio endgame PV outbreaks reflect serious gaps in immunity to PV due to the weakness of routine immunization coverage in otherwise polio-free countries, all countries should maintain uniformly high immunization coverage at the district level to minimize the consequences of any virus introduction. Keeping strong and encouraging both AFP surveillance and ES all over the world is crucial to ensure the PV will not return unnoticed and, finally, to achieve the global eradication goal.