MBL2 and viral infectious disease: Despite these shortcomings, the possibility that specific variants of the MBL2 gene known to influence serum MBL levels appear to be associated with severe bacterial co-infection is an intriguing finding deserving of additional study, especially given the prevalence of co-infection among case-patients who died of pandemic (H1N1) 2009 virus infection (38) and observations that children co-infected with influenza and S. aureus may have higher case-fatality rates (39).