A Prospective Multicenter Study of Leukopenia in Infants Younger Than Ninety Days With Fever Without Source

Little is known about the value of leukopenia for assessing the risk of having a bacterial infection in young febrile infants.

Infants younger than 90 days with fever without source were prospectively recruited between October 2011 and September 2013 in 19 Spanish Pediatric Emergency Departments. We analyzed the prevalence of invasive bacterial infection (IBI, positive blood or cerebrospinal fluid culture) and non-IBI (urinary tract infections and any other microbiologically confirmed bacterial infection excluding IBIs) by leukocyte count and general appearance.

Among the 3401 infants recruited, 680 were diagnosed with non-IBIs (19.9%) and 107 with IBIs (3.1%). Overall, 244 infants had leukopenia (<5000 cells/mcL), 2369 a normal leukocyte count and 790 leukocytosis (>15,000 cells/mcL). Among the 3034 well-appearing patients, those with leukopenia had a lower prevalence of non-IBI [8.1% vs. 14.7%; odds ratio (OR) 0.51 (95% confidence interval (CI): 0.29-0.88)] and a similar prevalence of IBI [2.5% vs. 2.0%; OR, 1.20 (95% CI: 0.44-3.44)] compared with those with a normal leukocyte count. Among the 367 not-well-appearing infants, those with leukopenia had a similar prevalence of non-IBI [8.9% vs. 14.7%; OR, 0.57 (95% CI: 0.16-1.79)] and a higher prevalence of IBI [17.8% vs. 6.9%; OR, 2.90 (95% CI: 1.06-7.78)]. In the subgroup of well-appearing infants 22-90 days old without leukocyturia according to urine dipstick results, prevalence of both non-IBIs and IBIs was similar in patients with leukopenia and those with a normal leukocyte count.

Leukopenia in well-appearing young febrile infants should not be considered a risk factor for having a bacterial infection.