BACKGROUND: Indoor human environments, including homes, offices, schools, workplaces, transport systems and other settings, often harbor potentially unsafe microorganisms. Most previous studies of bioaerosols in indoor environments have addressed contamination with bacteria or fungi. Reports on the presence of viral aerosols in indoor air are scarce, however, despite the fact that viruses are probably the most common cause of infection acquired indoor. OBJECTIVE: This review discusses the most common respiratory (influenza viruses, rhino-viruses, coronaviruses, adenoviruses, respiratory syncytial viruses, and enteroviruses) and gastrointestinal (noroviruses) viral pathogens which can be easily transmitted in indoor environments. RESULTS: The vast majority of studies reviewed here concern hospital and other health facilities where viruses are a well-known cause of occupational and nosocomial infections. Studies on other indoor environments, on the other hand, including homes, non-industrial workplaces and public buildings, are scarce. CONCLUSIONS: The lack of regulations, threshold values and standardized detection methods for viruses in indoor environments, make both research and interpretation of results difficult in this field, hampering infection control efforts. Further research will be needed to achieve a better understanding of virus survival in aerosols and on surfaces, and to elucidate the relationship between viruses and indoor environmental characteristics.

Among microorganisms, viruses are best fit to become emerging pathogens since they are able to adapt not only by mutation but also through recombination and reassortment and can thus become able to infect new hosts and to adjust to new environments. Enteric viruses are among the commonest and most hazardous waterborne pathogens, causing both sporadic and outbreak-related illness. The main health effect associated with enteric viruses is gastrointestinal illness, but they can also cause respiratory symptoms, conjunctivitis, hepatitis, central nervous system infections, and chronic diseases. Non-enteric viruses, such as respiratory and epitheliotrophic viruses are not considered waterborne, as they are not readily transmitted to water sources from infected individuals. The present review will focus on viral pathogens shown to be transmitted through water. It will also provide an overview of viruses that had not been a concern for waterborne transmission in the past, but that may represent potentially emerging waterborne pathogens due to their occurrence and persistence in water environments.

I virus sono tra i principali agenti di infezioni emergenti, in quanto sono in grado di acquisire nuove caratteristiche biologiche attraverso fenomeni di mutazione, ricombinazione e riassortimento genico, adattandosi così a nuovi ospiti e nuove nicchie ecologiche. I virus enterici sono tra le principali cause di malattie infettive di origine idrica, che possono manifestarsi come casi sporadici o cluster epidemici. Le manifestazioni cliniche più comuni sono le gastroenteriti; tuttavia i virus enterici sono in grado di causare anche sintomi respiratori, congiuntiviti, epatiti, infezioni del sistema nervoso centrale e malattie croniche. La presente rassegna fornisce una panoramica dei virus enterici tradizionalmente associati alle malattie idrotrasmesse; mostra inoltre dati epidemiologici su alcuni gruppi di virus che non sono stati associati a malattie idrodiffuse in passato (inclusi virus respiratori ed epiteliotropici), ma che possono rappresentare nuovi patogeni emergenti a causa della loro presenza e persistenza in ambienti acquatici.

The prevalence of enteric viruses in wastewater, the efficacy of wastewater treatments in eliminating such viruses, and potential health risks from their release into the environment or by recycling of treated wastewaters, are very important issues in environmental microbiology. In this study we performed a quantitative TaqMan real-time PCR (polymerase chain reaction) analysis of enteric viruses on samples of influents and effluents from 5 wastewater treatment plants in and around Rome. Three epidemiologically important, waterborne enteric viruses were analyzed: adenoviruses, enteroviruses and noroviruses (GI and GII) and compared to classical bacterial indicators of fecal contamination. The concentration of adenoviruses was the highest, in both raw and treated waters. Mean values in influents were ranked as follows: adenovirus > norovirus GI > norovirus GII > enterovirus. In effluents, the ranking was: adenovirus > norovirus GI > enterovirus > norovirus GII. Removal efficiencies ranged from 35% (enterovirus) to 78% (norovirus GI), while removal efficiency for bacterial indicators was up to 99%. Since molecular quantification does not necessarily indicate an actual threat to human health, we proceeded to evaluate the infectivity of enterovirus particles in treated effluents through integrated cell culture and real-time PCR. Infectivity assays detected live virions in treated water, pointing to potential public health risks through the release of these viruses into the environment. A better understanding of viral presence and resistance to sewage purification processes have the potential of contributing to the effective management of risks linked to the recycling of treated wastewater, and its discharge into the environment.

La prevalenza dei virus enterici nei liquami urbani, la loro rimozione durante i trattamenti di depurazione delle acque reflue, e rischi potenziali per la salute legati alla contaminazione degli ambienti idrici o al riutilizzo delle acque depurate, sono argomenti di grande interesse in microbiologia ambientale. In questo studio abbiamo stimato la concentrazione di virus enterici, in campioni di reflui grezzi e depurati di 5 impianti di trattamento di reflui urbani localizzati in Roma e dintorni, utilizzando metodologie quantitative molecolari (TaqMan real-time PCR). Sono stati analizzati tre gruppi di virus enterici responsabili di epidemie di origine idrica (adenovirus, enterovirus e norovirus GI/GII), parallelamente ai classici indicatori batterici di contaminazione fecale. Le concentrazioni virali più elevate sono state rilevate per gli adenovirus, sia nei reflui non depurati sia in quelli trattati. Nei reflui grezzi sono state osservate le seguenti concentrazioni medie: adenovirus > norovirus GI > norovirus GII > enterovirus; negli effluenti depurati: adenovirus > norovirus GI > enterovirus > norovirus GII. L'efficienza di rimozione virale variava dal 35% (enterovirus) al 78% (norovirus GI), mentre per gli indicatori batterici raggiungeva il 99%. Poiché i metodi molecolari non forniscono indicazioni circa l'infettività dei virus rilevati, si è proceduto a valutare la capacità di replicazione delle particelle virali (limitatamente agli enterovirus) nei liquami depurati utilizzando un sistema integrato colture cellulari/real-time PCR. L'analisi ha rilevato particelle virali infettive, indicando potenziali rischi per la salute pubblica legati alla contaminazione dei corpi idrici recettori. Una migliore comprensione della resistenza dei virus ai processi di depurazione è importante per la gestione dei rischi legati al riutilizzo delle acque reflue trattate, o alla loro immissione nell'ambiente.