Simkania negevensis, a recently found Chlamydia-like organism, has been associated with respiratory infections in children and adults with pneumonia, but S. negevensis findings have been common also without any infection. The aims of the present paper were to evaluate S. negevensis in the aetiology of paediatric community-acquired pneumonia (CAP), its seroprevalence in north Italian children, and whether there is cross-reactivity between S. negevensis and Chlamydia pneumoniae serology. Antibodies to S. negevensis were measured by microimmunofluorescence (MIF) in 101 frozen paired sera obtained from children with CAP. Serological evidence (>/=4-fold increase or decrease in IgM or IgG) of acute S. negevensis infection was achieved in 5 (5%) cases. Two were mixed infections with Mycoplasma pneumoniae and 1 with respiratory syncytial virus. In total, 20-30% of the children had measurable antibodies to S. negevensis, with no association with age. No cross-reactivity was observed between antibodies to S. negevensis and C. pneumoniae. S. negevensis appears to be a real, though rare, cause of CAP in children.
