This requires further investigation, in particular comparison with an asymptomatic HCW group. We believe that these results may have occupational health implications for HCWs, given the body of evidence that supports a complex, synergistic and poorly understood pathogenic relationship between bacterial and viral respiratory infection (Klugman et al., 2009, Madhi and Klugman, 2004, MMWR, 2009 and Zhou et al., 2012). The finding that bacterial colonization and co-infections were a greater risk on respiratory wards than other clinical settings

also supports the fact that occupational transmission is occurring in HCWs. Selleck HKI-272 Interestingly, smoking was not a risk factor for colonization or co-infection. We also found that nurses had significantly higher rate of bacterial co-infection than doctors. This may be due to higher patient contact or differences in use of infection control measures and personal protection (Chan, 2010 and Chan et al., 2002). The clinical significance of bacterial colonization in HCWs is uncertain, and this is an under-studied and unrecognized risk in HCWs. The significant PLX 4720 protection against this afforded by N95 respirators mirrors the same trend seen in our previous study for clinical

outcomes (MacIntyre et al., 2011 and Macintyre et al., 2013). Outbreaks of bacterial respiratory infection do occur in HCWs (Kleemola and Jokinen, 1992, Ong et al., 2006 and Pascual et al., 2006). Therefore, the observed reduction in bacterial colonization may translate to clinical protection against infection. S. pneumoniae was the most common bacteria identified in the upper respiratory tract. Invasive pneumococcal disease is thought to occur shortly after acquisition of colonization ( Boulnois, 1992 and Gray et al., 1980), and the infection can be transmitted by a colonized, asymptomatic individual. The rate of pneumococcal colonization demonstrated in our study was 6% (30/481 in controls), which is within the range described in adults

(who have lower rates of colonization than children) ( Austrian, 1986, Kadioglu et al., Terminal deoxynucleotidyl transferase 2008, Obaro et al., 1996 and Ridda et al., 2011). In an earlier study of frail elderly adults, only 1/315 subjects carried S. pneumonia ( Ridda et al., 2011), although rates of adult carriage in the pre-vaccine era of up to 28% have been described ( Hammitt et al., 2006). Bacterial load in the nasopharynx, not measured in this study, may be important in predicting the risk of invasive disease or viral co-infection and warrants further study ( Klugman et al., 2009). We demonstrated that N95 respirators prevent carriage with S. pneumoniae. Although S. pneumoniae is not typically associated with outbreaks, nosocomial transmission and invasive disease in hospital patients from a carrier HCW have been reported ( Guillet et al., 2012).