Based on these findings, in the present study, we examined the relationship between the global Quorum regulatory network (QS/QQ) mediated by the abaR (QS) and aidA (QQ) genes and the development of pneumonia and bacteraemia in clinical strains of A. baumannii isolated in the “II Spanish Study of A. baumannii GEIH-REIPI 2000-2010,” a multicentre study involving 45 Spanish hospitals and 246 patients. This evidence concerns the gene AIDA and pneumonia.