Numerous outbreaks of Acinetobacter baumannii (Ab) have been reported, most commonly in intensive care units, surgical wards, or among burn patients. Ab is a Gram-negative coccobacillus capable of colonizing the skin, the gastrointestinal tract, and the oropharynx in humans. Its pathogenicity is low, and it causes nosocomial infections (pneumonia, bacteremia, surgical site infections, or urinary tract infections) in severely compromised patients. Transmission occurs primarily via hand-to-hand contact between patients, with the environment serving as a secondary reservoir. The strains responsible for nosocomial outbreaks are often multidrug-resistant, limiting the number of antibiotics available, particularly for probabilistic antibiotic therapy. The impact of Acinetobacter on mortality is controversial. The severity of the underlying condition is the most common independent risk factor for mortality during outbreaks. In France, during the 2001 national prevalence survey of nosocomial infections, Ab accounted for 1.2% of microorganisms isolated from nosocomial infections. In October 2001, an outbreak of an Ab strain producing a VEB-1 type extended-spectrum beta-lactamase (ESBL) that occurred in the intensive care unit was reported to the CClin and the Departmental Directorate of Health and Social Affairs (Ddass) by the Valenciennes Hospital Center. It involved 20 cases with 12 deaths, 4 of which were directly attributable to the infection. In 2003, the same strain was identified again in several healthcare facilities in the Nord-Pas-de-Calais (NPC) region. This article describes the triggering of the alert, the investigations, and the control of the regional spread of this multidrug-resistant bacterium (MDRB). (R.A.)