Nosocomial Bacteremia in Children: A 15‐Year Experience at a General Hospital in Mexico
Objective. To describe the incidence and etiology of nosocomial bloodstream infections in children at a general hospital.
Design. Review of nosocomial bloodstream infections detected in children during 1991‐2005. Data were prospectively gathered through active surveillance. Annual rates of infection were compared.
Setting. A public general hospital in San Luis Potosi, Mexico.
Patients. Children younger than 15 years of age admitted to pediatric wards and subjected to prospective surveillance for nosocomial infection.
Interventions. Measures instituted to decrease the incidence of hospital‐acquired infection during the 15‐year study period included establishing active surveillance for hospital‐acquired infection, reinforcing compliance with handwashing recommendations, decreasing the degree of crowding on wards, establishing guidelines for the management of intravenous catheters and solutions, preparing parenteral nutrition and intravenous solutions under a laminar air‐flow hood, and increasing nursing personnel.
Results. There were 868 nosocomial bloodstream infections detected in 29,273 subjects (overall rate, 2.94 episodes per 100 discharges). Infection rates were greatest among children admitted to the neonatal intensive care unit and lowest for those admitted to the school‐age ward and the infectious diseases ward. There was a significant decrease in rates of nosocomial bacteremia in all of the wards. The organisms isolated most commonly were Klebsiella pneumoniae, Candida species, and coagulase‐negative staphylococci. Mortality rates were higher for children with a gram‐negative bacterial bloodstream infection (45.2%) and lower for children with a gram‐positive bacterial infection (19.2%).
Conclusions. Rates of nosocomial bloodstream infection decreased over the past 15 years at our hospital but continue to cause significant mortality. Continuing efforts to decrease the frequency of and mortality due to bloodstream infection are warranted.
Received February 23, 2006; accepted April 24, 2006; electronically published March 9, 2007.
Hospital‐acquired infections are a leading cause of morbidity in hospitals. Bloodstream infections are among the most common hospital‐acquired infections in children.1 In addition, bloodstream infections have high mortality rates, highlighting the importance of preventive measures.2 An active infection control program can identify in a timely manner the occurrence of these infections and establish control measures. Data from Mexico regarding nosocomial infections in children are scarce. At the Hospital Central “Dr. Ignacio Morones Prieto” (San Luis Potosi, Mexico), an infection control committee was established in 1991. We reviewed the incidence and microbiological features of hospital‐acquired bloodstream infection recorded in pediatric patients at this institution during 1991‐2005.
Methods
Hospital Characteristics
The Hospital Central “Dr. Ignacio Morones Prieto” is a general hospital that serves as a referral center for the state of San Luis Potosi and nearby areas. There are 13 specialty or subspecialty training programs at the hospital. In addition, medical students attend the hospital for training. The pediatric department provides specialty care in the following areas: cardiology, surgery, gastroenterology, hematology, infectious diseases, pulmonology, neonatology, nephrology, neurology, oncology, and intensive care. The pediatric wards include 71 beds and comprise the following areas: a neonatal intensive care unit (NICU), which includes intensive care, intermediate care, and growth and development areas; a toddler ward; a school‐age ward; and an infectious diseases ward. Since 2001, there has been a dedicated pediatric intensive care unit.
Calculation of Nosocomial Bloodstream Infection Rates
The infection control committee was established in 1991 at the Hospital Central “Dr. Ignacio Morones Prieto.” Since then, active surveillance to detect hospital‐acquired infection has been performed in all wards in the hospital, including the pediatric wards. To identify bloodstream infection, computerized records kept by the infection control committee were reviewed. Nosocomial bacteremia rates were calculated on the basis of cases identified through active surveillance and the annual number of discharges from each ward.
Bacteremia Definition
In the pediatric department, children with suspected sepsis or fever onset during hospitalization usually have blood cultures performed for bacteremia detection. Bloodstream infections were defined according to surveillance definitions established by the Mexican health authorities.3 The presence of bacteremia was defined as the isolation of a pathogen from a blood culture performed for a patient with symptoms suggestive of infection. For patients with blood cultures in which coagulase‐negative staphylococci were isolated, diagnosis of bacteremia required at least 2 blood cultures positive for the same organism; for patients with clear evidence of sepsis and no other explanation except the isolation of coagulase‐negative staphylococci from a blood culture, a single positive blood culture result was considered sufficient for the diagnosis of bacteremia.
Activities Performed by the Infection Control Committee
During the 15 years of the study, several measures were instituted to decrease hospital‐acquired infections. On March 1, 1991, active surveillance for hospital‐acquired infections was established. Active surveillance activities include visits by infection control committee personnel to all hospitalized patients at least 3 times per week to identify clinical findings suggesting the presence of nosocomial infection, daily recording of positive culture results reported by the microbiology laboratory, and monthly infection control committee meetings. During 1994‐1996, the following infection control measures were put into place: reinforcement of compliance with handwashing recommendations, reduction of the degree of crowding in the toddler ward and the NICU, and implementation of guidelines for the management of intravenous catheters and intravenous solutions. Starting in February 1994, total parenteral nutrition was prepared using a laminar air‐flow hood, and intravenous infusion sets were changed at preset intervals. Starting in 1998, all intravenous fluids for pediatric patients, except fluids ordered as “urgent,” were processed under the laminar air‐flow hood. During 2001‐2005, the number of nursing personnel was increased.
Statistical Analysis
Nosocomial bacteremia rates were compared by the χ2 test or the χ2 test for trend. A P value of less than .05 was considered statistically significant. Statistical analysis was performed using the R statistical package, version 2.1.0 (R Foundation for Statistical Computing), and Epi Info, version 3.3.2 (Centers for Disease Control and Prevention).
Results
Nosocomial Bacteremia Rates
During the study period, 29,273 patients were discharged from the pediatric wards and actively surveyed (8,420 patients from the toddler ward, 15,079 from the school‐age and infectious diseases wards, 5,041 from the NICU, and 733 from the pediatric intensive care unit). There were 868 nosocomial bacteremia episodes identified during the 15‐year period. The mean annual rate of nosocomial bacteremia was 2.94 episodes per 100 discharges. Nosocomial bacteremia rates according to the year of study are shown in Figure 1. There was a significant decrease in nosocomial bacteremia rates: during the first year of surveillance (1991), the nosocomial bacteremia rate for pediatric patients was 3.69 episodes per 100 discharges, whereas during the last year of the study (2005), the rate was 1.8 per 100 discharges (
by the χ2 for trend). Figure 2 shows the nosocomial bacteremia rates for the different wards. There were significant differences observed between wards. The NICU showed the highest rates, followed by the pediatric intensive care unit and toddler ward; the lowest rates were observed in the school‐age and infectious diseases wards. The χ2 test for trend revealed a significant decrease in nosocomial bacteremia rates in all wards (NICU, 
; toddler ward, 
; school‐age and infectious diseases wards, 
; and pediatric intensive care unit, 
).
Figure 1. Rates of nosocomial bacteremia among pediatric patients at a general hospital in San Luis Potosi, Mexico.
Figure 2. Linear regression curves showing nosocomial bacteremia rates in a neonatal intensive care unit (diamonds), a pediatric intensive care unit (circles), a toddler ward (squares), and school‐age and infectious diseases wards (triangles) at a general hospital in San Luis Potosi, Mexico.
Information regarding days of intravascular catheter exposure for pediatric patients was available from 1997 onward. The overall number of intravascular catheter–days for children increased during the study period (1,141 intravenous catheter–days were registered in 1997, and 5,035 were registered in 2005). We also analyzed the mean length of stay for pediatric patients hospitalized during 1994‐2005. The mean length of stay was shorter for patients admitted during 2002‐2005 (9.1 days) than for patients admitted during 1994‐2001 (11.4 days). The decrease in length of stay was observed in all wards except the NICU, where no overall change in length of stay was recorded between 1994 and 2005.
Microorganisms Isolated in Blood Cultures
Bacteria isolated in blood cultures during the study period are summarized in Table 1. Gram‐negative bacilli were the most common organisms isolated from pediatric patients with nosocomial bacteremia. We divided the study period into 5‐year intervals and compared the types of organisms that were isolated (Table 2). There was an increase in the percentage of cases caused by gram‐positive organisms and a decrease in the percentage of cases caused by Candida species between the first and third 5‐year periods. The proportion of cases caused by gram‐negative organisms varied over the years but did not show a definite trend.
Mortality Associated With Nosocomial Bacteremia
The discharge status (ie, alive vs dead) of patients with nosocomial bacteremia was analyzed. Crude mortality was estimated, because it was not possible to distinguish between bacteremia‐associated mortality and mortality related to other causes, on the basis of the infection control committee records. The overall mortality rate among children with nosocomial bacteremia was 37.7% (327 of 868). There was not a significant difference in the mortality rate throughout the study period (
by the χ2 test for trend). The mortality rate among children admitted to the hospital who did not present with nosocomial bacteremia was 5.3%. There were significant differences in mortality rates according to the type of organism (ie, gram‐negative bacteria, gram‐positive bacteria, or Candida species) responsible for the bacteremia episode (
). The mortality rate was lowest among subjects with bacteremia caused by gram‐positive organisms (19.2%) and highest for subjects with bacteremia caused by gram‐negative organisms (45.2%); patients with fungemia had an intermediate mortality rate (35.8%).
Discussion
Nosocomial infections are an important problem in current healthcare delivery. Because of the complexity of medical treatments available today, the number of risk factors for hospital‐acquired infections has increased. Intensive care units have higher rates of nosocomial infections than other wards. This is explained by the need to perform invasive interventions to treat the complex and severe disorders of patients hospitalized in intensive care units. In pediatric wards, NICUs represent a particular problem because of the immature immune systems and deficient physical barriers of the patients, the frequent use of intravascular catheters and parenteral nutrition, and prolonged hospital stays. Thus, it is not surprising that infection rates observed in this population are among the highest registered for different types of intensive care units.4 Nosocomial bacteremia episodes contribute significantly to patient morbidity and mortality. Therefore, monitoring of nosocomial infection rates is of great importance to establish preventive measures.
Most reports on nosocomial infections in pediatric patients from Mexico include all infections. Avila‐Figueroa et al.5 studied the prevalence of nosocomial infection in several pediatric hospitals, using a 1‐day survey. The prevalence of nosocomial infection among children was 9.8% in that study; 19% of these infections were described as sepsis or bacteremia. Avila‐Figueroa and colleagues observed large variability in infection rates, according to hospital size and the complexity of disorders treated in different hospitals. Muñoz et al.6 reported the frequency of nosocomial bacteremia among pediatric patients at a general hospital in León, Mexico, and documented a decrease in the infection rate between 1992 and 1997. Nosocomial bacteremia rates in our hospital were 3.69 cases per 100 discharges at the beginning of the study and 1.8 cases per 100 discharges in 2005; these rates are comparable to those observed by Muñoz et al.6 (3.12 cases per 100 discharges at baseline and 1.54 cases per 100 discharges during the last year in their study). Nevertheless, there are several limitations when comparing nosocomial infection rates between hospitals. Factors that have an important association with nosocomial infection rates, such as age, complexity of illness, and hospital size, vary between hospitals.5 Therefore, it may be more important to compare rates observed in the same institution over several years than to compare rates between hospitals. Comparison of current nosocomial infection rates to those observed in the past allows evaluation of infection control measures, prompt identification of outbreaks, and establishment of control measures to limit the number of infections.
During 1991‐2005, several interventions were performed by the infection control committee that probably led to the decrease in nosocomial infections. Specific interventions to decrease the risk of bloodstream infection included preparation of intravenous fluids under a laminar air‐flow hood, frequent changes in infusion sets and venopuncture sites, and surveillance of intravenous catheter management. In addition, other measures known to decrease overall rates of hospital‐acquired infection were instituted, such as reinforcing compliance with handwashing recommendations and decreasing the degree of crowding on wards. Of note, the number of intravascular catheter–days for children increased between 1997 and 2005; therefore, the decrease in nosocomial bacteremia rates does not appear to be related to a decrease in the use of intravascular therapy. The decrease in the length of stay observed during the later years of the study probably contributed to the observed reduction in rates of nosocomial bacteremia. However, the reduction in the length of stay was more notable after 2001, and no reduction was observed in the NICU, indicating that other factors, in addition to a reduction in the length of stay, influenced the reduction of infection rates.
At our hospital, gram‐negative bacilli are the leading organisms associated with nosocomial bacteremia in pediatric patients. This finding is consistent with other reports from Mexico, although there is variability in the organisms observed at different hospitals. Some studies report gram‐negative organisms as the organisms most commonly responsible for nosocomial bacteremia, whereas others report coagulase‐negative staphylococci and other gram‐positive organisms as the pathogens most frequently responsible for hospital‐acquired infections.7‐11 Extrinsic contamination of intravenous fluids has been suggested as a possible explanation for the predominance of gram‐negative bacteria as the cause of nosocomial bacteremia.12 Although the use of a laminar air‐flow hood for preparation of intravenous fluids was instituted at our hospital, medications are mixed on the wards and could be a potential source for extrinsic contamination of fluids. In developed countries, gram‐positive organisms predominate, especially coagulase‐negative staphylococci.13‐16 These infections are frequently associated with the use of intravascular catheters. At our hospital, we observed a slight increase in the number of infections caused by gram‐positive organisms during the latter years of the study; this may be related to an increase in the use of intravascular catheters in intensive care units. However, we cannot determine whether this or other factors were responsible for this observation.
The overall mortality rate among children with nosocomial bacteremia was 37.7%. The high mortality rate we observed likely reflects the predominance of infections due to gram‐negative organisms, which are usually associated with higher mortality rates than infections caused by gram‐positive organisms.17‐20 Cases of bacteremia due to gram‐positive organisms were associated with a lower mortality rate, as has been reported in other populations.
In conclusion, we observed a significant decrease in nosocomial bacteremia rates in pediatric wards at our hospital over a 15‐year period. The creation and operation of an infection control committee allowed the hospital to monitor the occurrence of nosocomial infection and establish preventive measures, which have resulted in decreased rates of nosocomial infections. Efforts should continue in order to decrease the rate of bloodstream infections, as well as the mortality rate.
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