nosocomial infections are one of the most frequent causes of mortality and morbidity in children requiring intensive care including mechanical ventilation . in pediatric intensive care units ( picu ) , bloodstream and
they are almost always associated with prolonged use of invasive methods in the treatment of critically ill patients such as methods of catheterization and mechanical ventilation . according to the criteria of centers for disease control and prevention ( cdc criteria ) ,
one is the gram staining technique , which groups both micro - organisms and infections into gram - negative and gram - positive categories , and the other is incubation time , which distinguishes community from nosocomial infections . classifying infections is crucial in any infection surveillance program , in particular in the intensive care units ( icu ) . from the practical point of view
, time cut - offs , generally 48 h , have been accepted to distinguish community and hospital - acquired infections from infections due to micro - organisms acquired during the patient s stay in the icu ( i.e. , icu - acquired infections ) . however , many clinicians have appreciated that an infection developing after 48 h of icu stay , due to a micro - organism carried by the patient on admission to the icu , can not be considered as  true  icu acquired . obviously , this infection is nosocomial , i.e. the infection occurs in the icu because the patient required intensive care treatment for her / his underlying disease associated with the immuno - paralysis .
however , the causative micro - organism does not belong to the icu microbial ecology , as the patient imported the micro - organism in her / his admission flora . 
 
a new classification of icu infections , based on the knowledge of patient s carrier state , has been proposed .
this approach allows the distinction between imported , or primary , and secondary carriage of potentially pathogenic micro - organisms ( ppms ) , in addition to endogenous and exogenous infections .
the objectives of this study were to evaluate the incidence of infections and infection complications in children admitted to the picu , university childrens hospital , brno , czech republic during years 20042005 , to differentiate between primary endogenous ( pe ) , secondary endogenous ( se ) and exogenous ( ex ) infections , and to compare this classification with traditional classification of infections and identify the most common pathogens causing nosocomial infections at picu .
this prospective observational study included all the patients hospitalized for more than 3 days ( 72 hours ) at picu from jan 1 , 2004 to dec 31 , 2005 .
patients who had had the infection before the admission and those who did not develop an infection during the hospitalization were excluded from the study .  
surveillance samples of oropharyngeal and rectal swabs were obtained on admission to the picu , and twice weekly ( e.g. on mondays and thursdays ) thereafter .
diagnostic or clinical samples were obtained in the case of suspicion of infection based on the clinical condition and laboratory findings [ tracheal aspiration ( ta ) , bronchoalveolar lavage ( bal ) , blood , urine , smear , etc . ] .
the microorganisms causing the infections were classified based on their pathogenicity as potentially pathogenic microorganisms ( ppm ) such as streptococcus pneumoniae , haemophilus influenzae , moraxella catarhalis , staphylococcus aureus , escherichia coli , candida albicans , or pathogenic microorganisms ( pm ) such as klebsiella species , proteus species , morganella species , enterobacter species , citrobacter species , serratia species , acinetobacter species , pseudomonas species , stenotrophomonas species .
all the infections were classified based on the traditional classification of infections ( cdc criteria ) such as the cut - off interval ( infections appearing before or after 48 hours of hospitalization ) , and based on the carrier state .
knowledge of the carrier state , together with diagnostic cultures , allows the distinction between the three types of infection occurring in the icu .
primary endogenous infections ( pe ) were defined as an infection caused by ppm or pm brought into the unit with the patient who carried the ppm in throat and/or gut on admission .
secondary endogenous infections ( se ) was an infection caused by a ppm or pm not carried by the patient on admission , but acquired in the unit followed by oropharyngeal and/or gastrointestinal carriage and subsequent infection .
exogenous infections ( ex ) were infections caused by ppm or pm that was never present in throat and/or gut of the patient .
bacteria are transferred directly into an internal organ without previous carriage . according to this criterion ,
only secondary endogenous and exogenous infections are labeled icu - acquired infections , whilst primary endogenous infections are considered to be imported infections .
the patients were classified as having either infection at the time of admission or without infection .
the patients without infection at the time of admission were split into groups of those with complications caused by an infection and those without them .  
the study recorded following data for all the patients : age , weight , sex , pediatric risk of mortality ( prism ) score at admission , the basic cause of the illness , multiorgan failure score ( mofs ) , the length of the hospitalization , classification of the infections based on traditional classification of infections and carrier state criteria , the incidence of specific microorganisms , and the type of infection caused by them later on .
swabs of throat , nose and stool ( surveillance samples ) were qualitatively and semi - quantitatively processed in order to determine the carrier state type .
identification , typing and sensitivity of all the microorganisms were done using standard microbiological methods .  
descriptive statistics and basic statistical methods ( fisher exact test , pearson s chi - square test and mann - whitney u test ) were used for analysis of the findings depending on data type .
out of 617 patients admitted in the years 2004 and 2005 , 264 ( 42.7% ) patients were hospitalized for more than 72 hours . of the hospitalized patients , 86 ( 32.6% )
the study dealt with 178 ( 67.4% ) patients , who were without infection at the time of admission .
they included 22 boys and 22 girls with an average age of 88.1 months , average weight of 26.9 kg , and average length of stay 3.9 days .  

table 1 compares the patients with an infection during hospitalization and the patients without one .
both groups had similar demographic data including age , weight , sex and the cause of the basic illness , the severity of illness on admission ( prism , mofs ) , or mortality .
there was however , statistically significant difference in the length of stay ( 13.9 days for patients with an infection vs. 8.9 days for patients without an infection , p=0.0001 ) .
the distribution of the bacterial and yeast infections according to two classification schemes , namely 48 hour cut - off interval was based on traditional classification of infections ( cdc criterion ) and carrier state criterion .
the comparison of characteristics of the patients with and without nosocomial infection during hospitalization 
 fisher exact test ; pearson s chi - kvadrat test ; mann - whitney u test ; prism : pediatric risk of mortality ; mofs : multiorgan failure score based on the cdc criteria 70.5% of all the infections were classified as nosocomial and 29.5% of them as community infections . using the carrier state criteria , 27 ( 61.3% ) infections were classified as pe , 10 ( 22.7% ) infections as se and 7 ( 15.9% ) as ex .   in all three categories ( pe , se , ex ) , the most common one ( 95% [ 42 out of 44 infections ] ) was the lower airways infection ( table 2 ) .
primary endogenous and se in most cases were caused by ppm that can be carried by healthy people as well ( community bacteria ) .
primary endogenous infection in most cases ( 8 out of 24 ; 29.6% ) was caused by e. coli , and se was mostly ( 8 out of 10 , 80% ) caused by c. albicans .
the most common ex were klebsiella species and pseudomonas aeruginosa , which are the typical nosocomial pathogenous microorganisms .
the distribution of pathogens based on carrier state criterion pe : primary endogenous infections ; se : secondary endogenous infections ; ex : exogenous infections
the terms  exogenous  and  endogenous  , derived from the greek word  genous  , which mean  depend  or  develop  , and tell us whether the infections originated in the patient s inner or his outer environment .
there is no evidence that infections occurring on , or at a specific time after icu admission , are attributable solely to micro - organisms transmitted via the hands of care givers and , hence , acquired during the icu stay .
it also still remains uncertain from the literature whether the given time cut - off refers to the number of days on the icu or the number of days following intubation .
the failure of the cdc guidelines to specify a time cut - off has led to the introduction of arbitrary and different time cut - offs , and to the use of the type of micro - organism causing the infections to distinguish between community- , hospital- , and icu - acquired infections .
clinicians , in extending the time cut - off , appreciated that infections developing in the first days after icu admission have nothing to do with the icu microbial ecology , and hence acknowledged that incubation time represents an inaccurate criterion for classifying infections in the critically ill patients . according to the pathogenesis of icu - acquired infections , acquisition of a ppm is followed by carriage and overgrowth of that micro - organism before colonization and infection of an internal organ may occur .
undoubtedly , this process takes more than 2 , 3 , or 4 days to develop .
therefore , a low respiratory tract infection due to a ppm already carried in the throat and/or gut on admission and developing in a ventilated trauma patient after 3 , 4 , or even 10 days of icu admission , can not be considered as icu acquired .
knowledge of the carrier state at the time of admission and throughout the icu stay is indispensable in distinguishing infections due to  imported  ppms ( i.e. , primary endogenous ) from infections due to bacteria acquired on the unit ( i.e. , secondary endogenous and exogenous ) .
icu - acquired infections , as the origin of the causative bacteria is outside the icu patient , the icu environment . in the case of the secondary endogenous infections , the micro - organism acquired in
the unit goes through a digestive tract phase , but this does not apply to the exogenous infections .
we consider the classification of infections developed in the hospital , and especially at icu , a key for the definition of nosocomial infections , because nosocomial infections lead to a higher mortality , prolong the hospitalization time , and increase the treatment costs . also , the percentage of occurrence of nosocomial infections is often a mark of quality of the critically ill patients treatment . in our set of patients ,
the infection developed during hospitalization prolonged the hospitalization time at the icu ( 13,9 vs. 8.9 day , p=0.0001 ) , and did not affect mortality ( 2 vs 10 patients , not significant ) .
since both patient groups namely , those with and those without an infection during hospitalization , are similar in terms of the demographic content and the severity of illness ( see table 1 ) , the prolongation of the hospitalization time must be caused by the infections .
in our set of patients the infections acquired during hospitalization were divided into two groups of nosocomial ( 70.5% ) and community ones ( 29.5% ) based on cdc criteria . the use of the carrier state criterion , however , led to significant differences in this classification resulting in the rate of 61.3% , for pe , 22.7% for se , and 15.9% for ex .
based on the carrier state , the se and ex infections are considered nosocomial , resulting in the total rate of nosocomial infections of 38.6% .
the evaluation of treatment quality of the critically ill children based on the percentage of nosocomial infections would be very different too .
another important aspect of this is the possibility to prevent the infections acquired during hospitalization .  
the main message of the traditionalists , who use a time cut - off of 48 h for classifying infection , is that the icu - acquired infectious problem is a huge early phenomenon involving about two - thirds ( up to 85% ) of all icu infections .
their approach implies that most infections occurring in the icus are nosocomial , due to micro - organisms transmitted via the hands of care givers , except those established in the first two days .
the 48 h time cut - off is also responsible for blaming staffs for almost all infections occurring in the icus and for initiating expensive transmission investigations .
therefore , hand washing is highly recommended by influential authorities , as the most important measure to control the exaggerated nosocomial problem due to an overestimated level of transmission .
our results show that more than 60% of all picu infections are primary endogenous , i.e. , due to micro - organisms not related to the icu ecology , and develop during the first week of icu stay .
hand washing can not be expected to control primary endogenous infections because it fails to clear oropharyngeal and gastrointestinal carriage of ppms present on arrival .
being inherently active solely on transmission , hand hygiene can not reduce the major infection problem of primary endogenous infection , as transmission is not involved in this type of infection . 
  strictly identifying and evaluating the primary endogenous , and the nosocomial problem of secondary endogenous and exogenous infections , the surveillance of both infection and carriage allows the intensivist to start with the appropriate prevention measures , protective isolation or the selective decontamination of the digestive tract .
based on the cdc definition of nosocomial infection , 70.5% ( 31 out of 44 patients ) had nosocmial infection , and based on the carrier state criterion 38.6% ( 17 out of 44 patients ) had the infection . given that the incidence of nosocomial infections is one of the factors affecting the quality of care for critically ill patients , the precise classification of the infection is crucial .
we believe that icu patients may benefit from an infection control program that includes surveillance of both carriage and infection
 
 background : the rate of nosocomial infection appears to depend on whether it is calculated using the center for disease control ( cdc ) or carrier state criteria . 
 the objective of this study was to differentiate between primary endogenous ( pe ) , secondary endogenous ( se ) and exogenous ( ex ) infections , and to compare this classification with cdc criteria for nosocomial infections . 
 
 methods : children hospitalized for more than 72 h at pediatric intensive care unit during 20042005 were enrolled . 
 children , who had the infection before the admission , and or did not develop an infection within the hospitalization were excluded . 
 surveillance samples were sampled on admission , and then twice a week . 
 diagnostic samples were obtained when infection was suspected based on the clinical condition and laboratory findings . 
 infections were evaluated as pe , se and ex , and their incidences were compared with cdc criteria for nosocomial infections . 
 
 results : one hundred seventy eight patients were enrolled in the study . 
 forty - four patients ( 24.7% ) develop infection . 
 twenty - seven patients ( 61.3% ) had pe , 10 patients ( 22.7% ) had se , and 7 patients ( 15.9% ) had ex infection . 
 secondary endogenous and ex infections are considered as nosocomial , thus 17 patients ( 38.6% ) had a nosocomial infection . 
 thirty - one patients ( 70.5% ) met cdc criteria for nosocomial infections . 
 seventeen patients ( 55% ) were classified as pe , and 14 patients ( 45% ) as se or ex infections . 
 
 conclusion : seventy percent of infections ( 31 out of 44 patients ) met the cdc criteria for nosocomial infections , but only 39% of infections ( 17 out of 44 patients ) were classified as nosocomial based on carrier state classification . 
Introduction
Materials and Methods
Results
Discussion
Conclusion
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