1. Bacterial and viral infections in patients requiring hospitalization : effect of mixed infections on clinical outcome J. Petitjean Lecherbonnier 1, F. Miszczak 1, C. Daurel 2, Dina 1, S. Gouarin 1, E.Pradier 1, A. Vabret 1 1 Laboratory of Virology, 2 Laboratory Microbiology, University Hospital caen, France BACKGROUND MATERIALS AND METHODSRESULTS Respiratory specimens: Our analysis included respiratory specimens collected between January 2010 and October 2012 from hospitalized patients (University Hospital of Caen and regional hospitals): 4887 children and 3343 adults - 7689 nasopharyngeal samples (NPS) found negative by the fast IFA and all the 527 bronchoalveolar lavages (BAL) were tested by MLPA RespiFinder® Assays. MLPA RespiFinder® Assay is a multiparameter molecular test which allow to detect and differentiate 21 respiratory pathogens (17 viruses + 4 bacterial pathogens) within 6 hours. 1-automatic extraction of 200µl of sample material (DSP Virus/Pathogen Minikit V1) were performed on QIAsymphony (Qiagen) 2-the RespiFinder®Smart 22 assay includes an internal amplification control and 3 steps: -Step1: pre-amplification which combines a reverse transcription with a PCR to amplify the target DNA (RT-PCR multiplex) -Step2: probe hybridization (combination of different probe labels and melting temperatures) -Step3: probe ligation step and probe amplification The detection is accomplished by analysis of specific melting peaks on RotorGene instrument on three different channels We detected 3695 positive respiratory specimens (45%) including 3577 viral infections, 78 bacterial infections and 40 mixed infections. Viral coinfection with two, three or four pathogens were detected in 455 specimens (12,7%). There is no mixed infection in BAL. In the 40 mixed infections, the bacterial pathogens detected were 80% Mpn, 10% Chlamydophila pneumoniae (Cpn), 10% Bordetella pertussis (Bper) Eight different viruses were identified in mixed infections: the most frequent are 57,5% enterovirus/rhinovirus (EV/RV), 20% coronavirus (CoV) and 15% adenovirus (AdV); other detected viruses are respiratory syncytial virus (RSV), bocavirus (BoV), human metapneumovirus (hMPV), parainfluenza virus 2 and 3 (PIV2, PIV3). Children are mainly affected by mixed infections (90%) with a sex-ratio M/F of 1,9 Clinical data collected from 31 patients showed 25 lower respiratory tract infections (LRTI) and 6 upper RTI (UTRI), 15 children with asthma, 5 with sequential repeated viral episodes, 13 oxygenodependant, 4 with a respiratory distress and one died. The most frequent combinations are Mpn with EV/RV in asthma. In severe diseases, EV/RV is the most frequent virus associated with the three bacterial pathogens : Mpn, Cpn and Bper. Acute respiratory tract infections are a leading cause of hospitalization for children and adults. In order to determine the causative viral agents of these infections, we processed to the combination of the conventional immunofluorescence assays (IFA) and the multiplex realtime PCR assay (MLPA RespiFinder®, Pathofinder). Routine diagnosis revealed respiratory virus infection in 30% to 70%. Moreover, it allowed to describe a Mycoplasma pneumoniae (Mpn) outbreak in 2011 -12 including 35% of viral coinfections. In a retrospective analysis of the MLPA results, we evaluated the prevalence of viral and bacterial infections, the prevalence of mixed infections and the most frequent associations, the demographic and clinical data (gender, age, clinical final diagnosis, asthma and severity) CONCLUSION The MLPA RespiFinder®is a sensitive, specific, reliable and rapid molecular test for the detection of viruses and some bacterial respiratory pathogens. These findings underscore the higher frequency of mixed infections associating Mpn with EV/RV in children hospitalized from asthma but need to be investigated by further prospective studies. 23rd ECCMID-Berlin,2013