Bacteremia in infants: Time for a new approach?

Bacteremia is now a rare event in previously healthy children aged 3 to 36 months because of the introduction of routine immunization with the pneumococcal conjugate vaccine (PCV).

Since the introduction of the first 7-valent PCV (PCV7) in 2000, bacteremia rates in febrile children in an ambulatory setting dropped from prevaccinated rates of 1.6% to 4.3% to postvaccination rates of 0.16% to 0.37%.¹

Now, new data from a study by Kaiser Permanente Northern California (KPNC) show that the introduction in 2010 of an expanded 13-valent PCV (PCV13) for this age cohort continues to contribute to the annual reduction in bacteremia.1

Importantly, the study found that since the introduction of PCV13, the annual incidence rate of bacteremia occurring without a source dropped to 5 per 100,000 children, with 24% of cases occurring without a source.

Most cases of bacteremia (76%) occurred with a source, most frequently from urinary tract infections (34%), gastroenteritis (17%), pneumonias (8%), osteomyelitis (8%), and skin and soft tissue infections (6%).

“This study opens the door to additional discussions on our approach to healthy febrile toddlers,” says the lead author of the study, Tara L. Greenhow, MD, chair, Northern California Regional Chiefs of Pediatric Infectious Diseases, San Francisco, California.

Greenhow emphasizes that the findings of the study support adoption of new guidelines given the high percentage of bacteremia cases occurring with a source since the introduction of PCV13. “Therefore, performing a careful physical exam and obtaining a urinalysis and, if clinically appropriate, a stool culture should occur at the time of blood culture acquisition,” she says.

Drilling down

In the retrospective study, investigators reviewed electronic medical records of 57,733 blood cultures collected on children aged 3 to 36 months at KPNC between September 1998 and August 2014 to compare incidence rates of bacteremia prior to PCV7, post-PCV7 but prior to PCV13, and post-PCV13. All children had been seen in an outpatient clinic, emergency department (ED), or within the first 24 hours of hospitalization.

When comparing the incidence of bacteremia prior to PCV (1998/1999) and post-PCV13 (2013/2014), Greenhow and colleagues found that the annual number of bacteremia cases dropped by 78% and the annual number of pneumococcal cases dropped by 95.3%.

Using a time series analysis, the investigators found that the incidence of Streptococcus pneumoniae rates dropped from 74.5 (95% CI, 59-93) prior to PCV7 to 3.5 (95% CI, 1.1-8.7) post-PCV13 per 100,000 children per year. “This shows that the dramatic decline in S pneumoniae bacteremia rates was clearly related to the impact of immunization,” says Greenhow.

The study also looked at the most common pathogens causing bacteremia since the introduction of PCV13 and found that most cases are now caused by Escherichia coli (39%), followed by Salmonella spp (21%), and Staphylococcus aureus (17%).

“As the rate of pneumococcal bacteremia dropped by 95.3%, other causes of bacteremia are now more common than pneumococcus,” says Greenhow, adding that the rates of these other infections have not changed, “only their relative importance.”

The study found that the urinary tract was the source for 93% of the bacteremia caused by E coli.

Additional findings

The study also looked at the percentage of contaminant organisms found in blood cultures throughout the study period and among the different sites (outpatient, ED, and first 24 hours of hospitalization. Overall, contaminant organisms were grown from 1.9% of blood cultures and remained constant throughout the 16 years of the study (1998-2014). “The rate of blood culture contamination did not change during our study years,” says Greenhow. “But as true bacteremia decreased, a greater proportion of positives were contaminants in the post-PCV13 period.” When looking at the different sites of culture acquisition, the study found that cultures taken in the ED and in the first 24 hours of hospitalization were significantly more likely to be contaminants than those taken in the outpatient clinic.

Overall, the study found that 58% of all blood cultures and 61% of all bacteremia were obtained in an outpatient clinic. Although the study found that the site of culture acquisition (ie, outpatient clinic, ED, or first 24 hours of hospitalization) was not a predictor for bacteremia, the numbers highlight that many children will present to clinicians’ offices.

“These results underscore the need for vigilance in all settings as the majority of children presenting with bacteremia were diagnosed in the clinician’s office,” says Greenhow.

REFERENCE

1. Greenhow TL, Hung YY, Herz A. Bacteremia in children 3 to 36 months old after introduction of conjugated pneumococcal vaccines. Pediatrics. 2017;139(4): e20162098. Available at: https://www.ncbi.nlm.nih.gov/pubmed/28283611. Accessed April 7, 2017.

Ms Nierengarten, a medical writer in Minneapolis, Minnesota, has over 25 years of medical writing experience, authoring articles for a number of online and print publications, including various Lancet supplements, and Medscape. She has nothing to disclose in regard to affiliations with or financial interests in any organizations that may have an interest in any part of this article.