Seasonality of Bacillus species isolated from blood cultures and its potential implications
published online 22 January 2009.
Background
Because they are rarely associated with actual infections, Bacillus species are usually defined as contaminants. However, when isolated, they require precise laboratory identification and may influence treatment.
Methods
Our aims were to examine the seasonality of Bacillus spp isolates cultured from clinical blood specimens. Blood culture results of several hospitals between December 1, 2003, and October 31, 2007, were analyzed. The data were aggregated by month of isolation and were also studied by age. Spectral and Cosinor analyses were used to examine the periodicity of the bacillus isolates.
Results
Of 931,331 blood cultures analyzed, 2487 (1.7%) yielded Bacillus spp isolates. There was a 2.5-fold increase in the number of bacillus isolates during August to October, compared with the other months (P < .01). This finding was consistent over hospitals and in all age groups. Spectral and Cosinor analyses confirmed this pattern.
Conclusion
Isolation of Bacillus spp from blood cultures has a seasonal pattern. This observation needs to be taken into account in surveillance systems for early detection of anthrax and in investigating nosocomial outbreaks. Elucidating the cause of this seasonality may enable future reduction in contamination rates.
aIsrael Center for Disease Control, Gertner Institute for Health Policy Research, Tel Hashomer, Israel
bDepartment of Clinical Microbiology and Infectious Diseases, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
eDepartment of Epidemiology and Preventive Medicine, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
Address correspondence to Liat Ashkenazi-Hoffnung, MD, Israeli Center for Disease Control, Ministry of Health, Gertner Institute, Sheba Medical Center, Israel 52621.
ABSTRACT