Shigella Bacteremia, Georgia, USA, 2002–2012

Shigella commonly causes gastroenteritis but rarely spreads to the blood. During 2002–2012, we identified 11,262 Shigella infections through population-based active surveillance in Georgia; 72 (0.64%) were isolated from blood. Bacteremia was associated with age >18 years, black race, and S. flexneri. More than half of patients with bacteremia were HIV-infected.


DISPATCHES
Shigella commonly causes gastroenteritis but rarely spreads to the blood. During 2002-2012, we identified 11,262 Shigella infections through population-based active surveillance in Georgia; 72 (0.64%) were isolated from blood. Bacteremia was associated with age >18 years, black race, and S. flexneri. More than half of patients with bacteremia were HIV-infected.
For 2002-2012, we identified 11,262 Shigella infections among Georgia residents. During this time, 10,806 (96.0%) of cultures were isolated from feces, and 72 (0.66%) were isolated from blood. We excluded 13 S. dysentariae (1 blood isolate) and 31 S. boydii (all fecal isolates) from further analysis. Patients with Shigella bacteremia were concentrated in the Atlanta metropolitan area (Table). Fifty-three (74%) blood isolates versus 3,089 (29%) fecal isolates were from patients >18 years of age. No bacteremia cases were outbreak-associated. Only 1 (0.87%) of 114 patients with documented international travel had bacteremia. Demographic variables significantly associated with bacteremia on bivariate analysis included male sex, black race, and residence in the Atlanta metropolitan area. Analysis of clinical variables demonstrated that patients with bacteremia were more likely to be hospitalized (61% vs. 17%; p<0.001) and to die (Table). Male sex, age >18 years, and S. flexneri serotypes remained significant on multivariate analysis.
Thirty-seven (51%) of the 72 patients with bacteremia were known to be HIV-infected. All but 3 HIVinfected patients resided in the Atlanta metropolitan area. Among those known to be HIV-infected, 92% were black, 97% had a known AIDS diagnosis, 97% were male, and 68% were known to be men who have sex with men (MSM), a risk factor for HIV acquisition.

Conclusions
The relative predominance of S. flexneri among blood isolates in comparison to fecal isolates in this analysis is noteworthy. In other large international series, S. flexneri has been identified in most bacteremia patients (5,8,9). More than half of the bacteremia patients in our study were known to be HIV-infected. Other researchers have noted the prominence of S. flexneri among MSM and HIV-infected persons (1,4,10,11). In data from South Africa, S. flexneri serotype 2a was also identified in 30% of invasive isolates (6). It is unclear whether these serotypes might have increased virulence or might be more common because of transmission networks, particularly among the HIV-infected patients in this study. It is clear, however, that HIV infection correlates with the epidemiology of Shigella bacteremia, particularly in the Atlanta area. Some of the demographic factors associated with bacteremia (e.g., black race, identification of S. flexneri) also were associated with HIV infection within the subset of patients with bacteremia. The predominance of the MSM risk factor among HIV-infected patients, along with the low infectious dose and possibility of sexual transmission of Shigella, make it possible that Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 26, No. 1, January 2020 123 we could be missing outbreaks within this population (7). Clinicians caring for HIV-infected patients should be aware of the possibility of Shigella bacteremia. Additionally, identification of Shigella bacteremia in an adult should prompt HIV testing unless another immunocompromising condition exists. Limitations of our study include the unavailability of epidemiologic and clinical data for all patients in the study. We had information about HIV status only for patients with Shigella bacteremia. Other clinical characteristics that might be associated with Shigella bacteremia were not collected and could not be analyzed (e.g., malignancy, transplantation) (4,10). Finally, some epidemiologic information and detailed identification of Shigella serogroups and serotypes was not available until 2005.
In summary, although S. sonnei predominated among fecal isolates in this study, similar numbers of S. sonnei and S. flexneri were identified in blood cultures. Shigella bacteremia, particularly when caused by S. flexneri, should prompt evaluation for a concomitant HIV infection among certain adult populations.