SORVEGLIANZA EPIDEMIOLOGICA E MOLECOLARE DELLA LISTERIOSI IN REGIONE LOMBARDIA, 2005 ¿ 2012

Listeriosis is a rare but severe disease emerging especially in fragile subjects, likely due to association with deprivation. Non pregnancy-related infections, food-acquired, mainly affect immunocompromised and older subjects. Considering the aging of national and regional population and the increase of immunosupressant therapy and pathologies is crucial to increase the knowledge about Listeria monocytogenes (L. monocytogenes) infection. The objectives of this study are: 1) describe listeriosis in Lombardy Region; 2) analyze L. monocytogenes strains with serotyping, Pulsed Field Gel Electrophoresis (PFGE), and MultiLocus Sequence Typing (MLST); 3) cross-match the information with capture-recapture method and statistical analysis. We analyzed the collected data over eight years (2005-12) from special laboratory surveillance network (LSN), comparing with Lombardy database of infectious disease (MAINF) data, reported over the same period and we underlined the critical points. In 2005-2012, 192 strains of L.monocytogenes were collected from laboratory network while 366 invasive listeriosis cases were notified to MAINF surveillance system. In the 2011 we observed an increase of cases either in the MAINF (i.e 73 cases) or in the LSN (i.e. 44 L. monocytogenes strains) database. The pregnancy-related cases were 24 (only one from a mother-child pair), while the non-pregnancy related ones were 168. The 36% of these 168 were over 65 years old and 83% had underlying risk factors (HIV, diabetes, neoplastic disease,…). Analyzing the L. monocytogenes strains we found that the most common serotypes were 1/2a (59.5%), 1/2b (9.1%), and 4b (28.1%). By using PFGE we realized that collected by LSN strains were characterized by 15 pulsotypes based on the PFGE profiles; 10 clusters were identified and the largest cluster included 39 isolated strains, identified along the whole considered period. The MLST technique gave twelve sequence types (ST). In the most numerous sequence type we recognised 39 L. monocytogenes strains; the ST number 21 was found in human cases but also in rodents. We compared two surveillance systems with the estimated amount of cases noting that the observed cases were underestimated. This tells us that our surveillance systems miss information. The statistical analysis underlined that the temporal distribution of cases was not random, but instead the cases concentrated in 2010 and 2011. The results of our surveillance work are satisfactory and we think that it is useful to compare and analyze the microbiological and epidemiological data coming from two sources to increase the statistics. The laboratory-based surveillance network of listeriosis can improve in sensitivity to better and more quickly detect cases, contribute to identify epidemic clones, and investigate the infection source.