Legionellosis outbreak associated with asphalt paving machine, Spain, 2009

Abstract

From 1999 through 2005 in Alcoi, Spain, incidence of legionellosis was continually high. Over the next 4 years, incidence was lower, but an increase in July 2009 led health authorities to declare an epidemic outbreak. A molecular epidemiology investigation showed that the allelic profiles for all Legionella pneumophila samples from the 2009 outbreak patients were the same, thus pointing to a common genetic origin for their infections, and that they were identical to that of the organism that had caused the previous outbreaks. Spatial-temporal and sequence-based typing analyses indicated a milling machine used in street asphalt repaving and its water tank as the most likely sources. As opposed to other machines used for street cleaning, the responsible milling machine used water from a natural spring. When the operation of this machine was prohibited and cleaning measures were adopted, infections ceased.

Figure 1

Timeline for epidemic of legionellosis, Alcoi, Spain, 2009. Light gray squares indicate days the paving machine was working; dark gray squares indicate incubation period; black squares indicate day of illness onset.

Figure 2

The 2 neighborhoods in Alcoi, Spain, with identified risk areas for the outbreak of legionellosis, 2009 (left). For each area, an enlarged map at right shows the common risk area (black lines) and the streets where the milling machine and water tank had operated during the incubation periods (gray lines).

Figure 3

Milling machine and water tank used for asphalt paving in Alcoi, Spain, 2009, during outbreak of legionellosis. The 2,000-L water tank (A, left circle) supplied the 18 atomizers (A, right circle; B, oval), which sprayed 8,000 L water/d.

Figure 4

Maximum-likelihood phylogenetic tree obtained from the concatenated alignment of 7 Legionella pneumophila genome loci obtained from clinical (C) and environmental (E) samples during outbreak of legionellosis in Alcoi, Spain, 2009. Isolates with identical sequence types (Table 1, Table 2) are represented as 1 isolate. Parentheses enclose the number of samples showing each sequence type. Reference sequences for Philadelphia, Paris, and Corby strains are included. Nodes supported by bootstrap values >70% are indicated. Scale bar indicates 0.002 nucleotide substitutions/position in the sequence.