Blood culture collection from outpatients < age 36 months with high fever (>40°C, rectal) became a standard of ambulatory care in Emergency Rooms (ERs) of the government Children's Hospitals in Chile's Metropolitan Region (MR) in 1999; thereafter, invasive pneumococcal disease (IPD) incidence doubled over preceding years' estimates limited to hospitalizations. We studied IPD among children with moderate (>39°C but <40°C, rectal) rather than high fever visiting Pediatric ERs. Recruitment ensued Monday to Friday, 1-5 PM, September 1, 2002 through August 31, 2003. Age <36 months; rectal temperature >39° but <40°C; outpatient management; parental consent for hemoculture were inclusion criteria. Thirteen-thousand five hundred seventy-seven children < age 36 months with moderate and 3,214 children with high fever sought ER care. Of 1,134 moderate fever children seen in ERs during the enrollment, parents of 837 consented (73.8%). During these days and hours, 714 children < age 36 months presented with high fever and 651 (91.2%) had a “routine” blood culture. Pneumococcemia was detected among 0.7% with moderate and 1.2% with high fever (6/837 vs 8/651, p > 0.05). Extrapolating these rates to all ER outpatients < age 36 months with moderate and high fever, we estimate the true burden as 95 and 39 cases, respectively. The burden of pediatric IPD in the MR is currently underestimated because bacteremias among ER outpatients with moderate fever are not detected. If blood cultures were systematically collected from outpatients with moderate fever, recorded pediatric IPD burden would rise >2-fold. However, economic and logistical constraints preclude such a practice.