Outcome of Staph aureus Bacteremia Similar in Neutropenic and Non-Neutropenic Patients

A prospective examination of over 2600 patients, some with abnormally low neutrophil counts, has not revealed a difference in their outcome compared with patients who are non-neutropenic when it comes to bacteremia caused by Staphylococcus aureus (S aureus). The 2 groups also appeared similar, clinically.

Although data has linked worse outcomes from S aureus bacteremia with the presence of prolonged and severe neutropenia, the data were acquired a while ago. “Data on clinical characteristics and outcomes of S aureus bacteremia in neutropenic patients with hematologic malignancy is limited to a few studies, which were published until the early 2000s. Since then, much progress has been made in the management and treatment of S aureus bacteremia,” wrote the investigators in their late-breaking poster presented today at ASM Microbe 2018 in Atlanta, Georgia.

The investigators rightly felt that the time had come to revisit the issue.

Presenter Byung-Han Ryu, MD, Gyeongsang National University Hospital, Gyeongsang, Korea, and colleagues from the Asan Medical Center, University of Ulsan College of Medicine, Seoul, prospectively compared the clinical characteristics and outcomes of S aureus bacteremia in neutropenic patients with hematologic difficulties (n = 64, 2.4%; 72% male), patients with neutropenic solid tumors (n = 24, .9%; 46% male), and non-neutropenic patients (n = 847, 32.4%; 62% male). The patients were treated at a single tertiary-care center.

Other differences between the 3 respective groups included the prevalence of nosocomial infections (81% vs 33% vs 51%), primary bacteremia (55% vs 25% vs 12%), delivery of appropriate antibiotics within the first 2 days of hospitalization in non-neutropenic patients (98% vs 100% vs 90%), and bacteremia lasting longer than 3 days in non-neutropenic patients (13% vs 17% vs 30%).

Similarities between the groups included median age (45.5 vs 58.5 vs 63 years), the prevalence of severe sepsis or septic shock (31% vs 25% vs 24%), and the prevalence of central venous catheter-related infections (23% vs 29% vs 25%).

Rates of mortality prior to discharge and within 30 days and 12 weeks of discharge were similar in the 3 groups.

The neutropenic hematologic patients often displayed nosocomial and primary bacteremia. The incidence of metastatic infections among the 3 patient groups was similar, being 17.2% in neutropenic hematologic patients, 16.7% in neutropenic solid tumor patients, and 20% in non-neutropenic patients. This finding contrasted with a description of the absence of metastatic infections in neutropenic patients with S aureus bacteremia.

Eradication of the primary site of infection was performed less often in the neutropenic hematologic patients. Still, the death rate in this group was no higher than that of the other 2 groups. Indeed, their 12-week mortality was significantly less than neutropenic solid tumor patients (15.6% vs. 45.8%; P = .003).

A multivariable analysis revealed independent associations between mortality and age (adjusted Odds Ratio [aOR] 1.03; 95% Confidence Interval [CI] 1.02-1.05; P<.001), Charlson comorbidity score (aOR 1.28, 95% CI 1.17-1.41; P<.001), Pitt bacteremia score (aOR 1.34, 95% CI 1.24-1.46; P<.001), pneumonia (aOR 2.79, 95% CI 1.59-4.88; P<.001), longer duration of bacteremia (aOR 1.68, 95% CI 1.13-2.48; P = .01), and metastatic infection (aOR 1.74, 95% CI 1.12-2.68; P =.01). Neutropenia in a hematologic malignancy was not an independent risk factor for 12-week mortality.

“Our findings suggest that clinical characteristics and outcomes of S aureus bacteremia in neutropenic hematologic patients are not significantly different from those in non-neutropenic patients,” the investigators wrote.

The results of patients treated at the 1 tertiary care center between 2008 and 2017 run counter to what might be expected intuitively and with what has been found for neutropenic cancer patients. In the latter, bloodstream infections caused by Gram-negative bacteria and Gram-positive bacteria, including S aureus, often carry a death sentence.

The reasons for the findings, particularly given prior findings that neutropenia is bad news for patients with bacteremia, presumably reflect advances in patient care over the past nearly 2 decades. This does remain in the realm of speculation, though, since the study was not designed to examine this.

Neutropenic patients typically are unable to mount a vigorous inflammatory response to infection, which can lay these patients open to serious infections that present minimal symptoms and signs. For example, fever may often be the only sign of infection.

The definition of neutropenia can vary depending on the institution. Typically, though, neutropenia is considered to be an absolute neutrophil count of fewer than 1500 cells per microliter. Severe neutropenia is usually defined as fewer than 500 neutrophils in the same volume, or an expected drop to that number within the next few days. The risk of clinically important infection increases as the neutrophil count falls below 500 cells per microliter, especially if neutropenia is prolonged.

DISCLOSURES

none

PRESENTATION

Poster CV1 LB1 presented Friday June 8.

Abstract Title: Clinical Characteristics and Outcomes Of Staphylococcus aureus Bacteremia in Neutropenic Patients with Hematologic Diseases: A 10-year Experience of a Tertiary-care Hospital

Byung-Han. Ryu, National University Hospital, Jinju, Republic of Korea

Brian Hoyle, PhD, is a medical and science writer and editor from Halifax, Nova Scotia, Canada. He has been a full-time freelance writer/editor for about 20 years. Prior to that, he was a research microbiologist and lab manager of a provincial government water testing lab. He can be reached at hoyle@square-rainbow.com.