Correspondence and Reprint requests : Dr. Murat Anil, M.D.
Mehmet Emin Gürkan Caddesi, Akasya apt. No: 10 Daire: 5
35410 Gaziemir, Izmir, Turkey. Fax: 00 90 232 433 07 56
[DOI- -10.1007/s12098- -009- -0083- -4]
[Received December 20, 2007; Accepted June 2, 2008]
Salmonella typhimurium Outbreak in a Neonatal Unit in
Murat Anil, Mehmet Helvaci, Nisel Ozkalay1, Esra Toprak, Ayse Berna Anil, Mustafa Dilek and
Department of Pediatrics and 1Department of Microbiology, Tepecik Educational and Research Hospital, Izmir,
Objective. To analyze an outbreak caused by a multipl resistant strain of S. typhimurium in a newborn unit in Turkey.
Methods. The outbreak occured during the period 15 to 29 March,2005. A newborn infected with S. typhimurium was defined
as a case. Newborns who were hospitalized during the outbreak period with no diagnosis of S. typhimurium infections
(n=50) constituted the control group I (CG I). The matched patients of the control group II (CG II) (n=20) were selected from
neonates without S. typhimurium infections during the period.
Results. Of 22 infants who were affected two died. Cases developed diarrhea (n=20), septicemia (n=5) and meningtis
(n=1). The strain was resistant to ampicillin, ceftriaxone, ceftazidime, amikacin, trimethoprim-sulfamethoxasole and
chloromphenicol, susceptible to meropenem. All of the infected neonates were treated with meropenem. The surveillance
cultures were negative. The outbreak was controlled by approprite therapy and institution of effective control measures. The
cases were more exposed to mechanical ventilation than CG I (p<0.05). The mean additional length of stay in cases was
significantly different from CG II (14.9 days vs. 5.1 days, p<0.05). The mean charges was $1588.78 for a case and $506.94
for a control (P<0.05). Accommodation accounted for 44.5% of these extra charges.
Conclusion. This study increases the understanding of the burden of multidrug-resistant S. typhimurium infection.
Nosocomial outbreaks have a major effect on healthcare delivery, costs and outcomes. [Indian J Pediatr 2009; 76 (6) :
629-633] E-mail: email@example.com
Key words : Neonates; Outbreak; Salmonella typhimurium; Risk factors; Additional length of stay; Extra charge
department of pediatrics of the Tepecik Educational and
Research Hospital, located in the city of Izmir, Turkey.
A case in the present study (n=22) was defined as a
patient with a stool/rectal swab and/or blood and/or
cerebrospinal fluid (CSF) culture positive for S.
typhimurium. Other newborns who were hospitalized
during the outbreak period with no diagnosis of S.
typhimurium infections (n=50) constituted the control
group I (CG I). An individual record was filled out with
the patient’s demographic data, along with possible
predisposing factors, including gender, birth weight,
age, gestational age, hospitalization duration, use of
antibiotics, mechanical ventilation, use of a central
venous catheter (CVC) and total parenteral nutrition
During the outbreak, stool specimens or rectal swabs
were collected from all patients (n=72), blood cultures
were taken from 32 neonates, and CSF cultures were
obtained from 5 neonates in the neonatal unit. A total of
78 samples from environmental surfaces, stool
Nontyphoidal salmonella (NTS) is one of the most
important enteric pathogens even in developed
countries. NTS may cause bloodstream and other
extraintestinal infections for which anti-microbial
therapy is required. The nosocomial spread of NTS,
particularly in neonatal wards, is known from the
literature.1- 4 In the present study we describe an outbreak
caused by a highly resistant strain of Salmonella
typhimurium that occurred in a newborn unit in Turkey.
The present study also investigated the outcome and the
economic burden attributable to this outbreak.
MATERIAL AND METHODS
The outbreak occurred in the neonatal unit of the
Indian Journal of Pediatrics, Volume 76—June, 2009629
Murat Anil et al
630Indian Journal of Pediatrics, Volume 76—June, 2009
specimens and swabs from the hands of all of the
working staff (32 health care personnel) were collected
in the neonatal unit. Also breast milk samples were
tested for Salmonella in this period. The isolates were
identified using standard laboratory methods5 and with
the BBL Crystal E/NF identification system (BD
Microbiology Systems, Sparks, MD) and were also
serotyped on the basis of somatic O, phase 1 flagellar,
and phase 2 flagellar antigens by an agglutination test
with antisera (Denka Seiken Co. Ltd, Japan) as specified
by the Kauffman-White scheme.6 The antimicrobial
susceptibility test was determined by the Kirby-Bauer
disk diffusion method according to the guidelines of the
clinical and laboratory standards institute susceptibility
criteria.7 The minimum inhibitory concentrations (MICs)
of the anti-microbial agents were determined by Etest
according to the manufacturer’s recommendations (AB
Biodisk, Solna, Sweden), and the extended-spectrum beta
lactamase (ESBL) phenotype was detected by using the
doubled-disk synergy method.2
The financial data on charges were retrospectively
retrieved from the hospital discharge abstracts
provided by the central financial service of the hospital.
The patients of the control group II (CG II) (n=20) were
selected from neonates without S. typhimurium
infections during the period. Comparing each case with
the matched control (control group II) permitted the
estimation of extra charges and extra length of hospital
stay. The matching criteria were birth weight (± % 10),
sex, gestational age (± 2 weeks), mechanical ventilation,
anti-microbial therapy, and use of CVC and TPN. All
but one of these factors was used as matched criteria.
Due to number of matching criteria, each case could be
matched for one patient only. The prolongation of the
length of stay due to the outbreak was obtained by
subtracting that of the case from that of the control
within each pair. Neonates who died due to S.
typhimurium infections (n=2) were excluded because of
the risk of underestimating costs and length of stay.
Categorical variables were compared by using the
likelihood ratio test or, when appropriate, using Fisher’s
exact test. Continuous variables were analyzed by the
student’s t-test, or the Wilcoxon Rank-Sum's test for non-
parametric distributions. A multivariate analysis using
the forward stepwise logistic regression method was
performed in order to identify risk factors associated
with the outbreak. The significance was defined at the
level of p≤0.05. SPSS version 11.0 (SPSS Inc, Chicago, IL,
USA) was used in the statistical analysis.
The outbreak began on 15th March 2005, with the
isolation of S. typhimurium from a 9-day-old newborn
(index case) hospitalized for newborn sepsis and
meningitis. The baby has been transferred from a local
hospital with suspicion of meningitis with a report of
antibiotic use. S. typhimurium was recovered from the
blood and CSF cultures. Once identified, the index case
was placed on isolation in a private room outside of
the unit. S. typhimurium was isolated from his mother’s
stools. The second affected baby appeared 3 days later.
Twenty patients had green or yellow loose to watery
stools, 2 had fever, 2 had hypothermia, and 2 had fever
and vomiting. Antimicrobial susceptibility tests
showed that all the S. typhimurium isolates were
resistant to ampicillin, ceftriaxone, ceftazidime,
chloromphenicol, and were susceptible to meropenem.
ESBL activity was detected in all isolates. After
receiving the anti-microbial susceptibility results, the
infected neonates were treated with meropenem. All
cases were placed in isolation in the intermediate-care
room unit, and the standard measures for the outbreak
control were instituted. All except 2 recovered, of
which one of them was an index case and had
meningitis and the diagnosis of the other case was
sepsis. No recurrence of the infection due to S.
typhimurium was found among the babies, and no other
cases were noted after 29th March 2005. None of the
surveillance cultures yielded S. typhimurium. The
attack rate of S. typhimurium infection during the
outbreak was 30.5 %. The characteristics of the 22 cases
are listed in Table 1.
TABLE 1. Characteristics of the 22 S. typhimurium Infected
Mean birth weight ± SD (g) 2010 ± 587
8.8 ± 2.8 (range: 5-14)
Mean age ± SD (day)
Sex ( / )
Positive specimens (Blood/Stool/CSF) 6 / 20 / 1
Outcome (death / recovery)2 / 20
The risk factors for S. typhimurium infection are
described in table 2. The use of antibiotics, the use of
CVC/mechanical ventilation, and TPN support were
statistically significant risk factors on univariate
analysis (p<0.05). By multivariate analysis, the use of
mechanical ventilation was found to be a risk factor for
S. typhimurium infection (odds ratio, 4.190; 95%
confidence interval, 1.240-14.157; (p=0.021).
Twenty cases were matched with the CG II. All
characteristics and co-morbidity were uniformly
distributed across both groups (p>0.05) (Table 3). In the
newborn unit, the average length of stay was 14.9±5.39
An Outbreak Caused by Salmonella Typhimurium in a Neonatal Unit in Turkey
Indian Journal of Pediatrics, Volume 76—June, 2009631
days (range : 9-28 days) for the cases, and 5.10±4.29
days (range : 2-20 days) for the CG II; thus the cases
stayed on average 9.85±4.67 days (range : 3-21 days)
longer than the CG II (p<0.05). After the occurrence of S.
typhimurium outbreak, the length of stay was 8.2±3.3
days (range : 7-15 days) and 4.1±4.0 days (range : 2-14
days) for the cases and the CG II, respectively (p<0.05).
The mean difference was 4.0±2.6 days.
The actual financial burden of the outbreak
(including fatal cases plus cost of surveillance cultures)
was $52,463.25. The average overall charges per patient
were $1,588.78 ± $1,460.37 in the cases and $506.94 ±
$559.97 in the CG II (p<0.05). The charges per day of stay
were significantly different for the cases and the CG II
($157.18 ± $41.45 vs $132.35 ± $24.90, p≤0.04). The
majority of the extra charges for patients with S.
typhimurium were accommodation (44.5%) and
personnel costs (24.5 %) (Table 4).
Control of Salmonella outbreaks in the neonatal settings
represents a challenge, sometimes requiring the closure
of the unit.8. The appropriate therapy of the affected
neonates and the institution of proper measures of
hygiene controlled the outbreak. Only the intermediate-
TABLE 3. Comparison of Patient’s Characteristics of Study
Characteristic Results (Mean or %)
CG II (n=20)Case (n=20)p*
Birth weight (g)
Gestational age (weeks)
*p≤0.05 (statistically significant), CG II, control group II; TPN;
total parenteral nutrition, CVC; central venous catheter.
TABLE 2. Univariate Analysis of Factors Associated with S. typhimurium Infection in the Neonates
OR 95 % CIp*
Weeks of gestation
Utilization of CVC
*p≤0.05 (statistically significant); CG I, control group I; TPN, total parenteral nutrition; CVC; central venous catheter; OR, odds ratio;
95% CI, 95% confidence interval
TABLE 4. Comparison of Charges for Subcategories Between Case and Controls
CategoryCharges in USA Dollars ($)
p Extra charges ($)
Laboratory and radiology costs
p≤0.05 (statistically significant); CG II, control group II.
Murat Anil et al
632 Indian Journal of Pediatrics, Volume 76—June, 2009
care room of the unit was closed to new admissions
during the outbreak period.
In previous literature, risk factors for developing
nosocomial infection include antibiotic use, use of CVC
and mechanical ventilation, and parenteral nutrition as
we determined.8-13 In the present study, the univariate
analysis revealed that the use of antibiotics, the use of
central venous catheter, the use of mechanical
ventilation, and TPN support are significantly related
to the S. typhimurium infection. The multivariate
analysis indicated that the use of mechanical
ventilation increased the hazard of S. typhimurium
infection in the neonatal ward.
One important aspect of this outbreak was the high
degree of anti-microbial resistance. For several years,
ESBL producing Salmonella spp. has become a
significant public health problem in many countries.1,14-
18 Because of its multi-drug resistance profile,
meropenem was given for treatment during this
outbreak. Molecular characterization of isolates could
not be done in this study. The identical antibiotic
susceptibility pattern and clinical information
suggested that an identical clone had been spreading in
The extra length of stay in the hospital is one of the
well-described parameters. Factors other than
nosocomial infection (e.g., birth weight and co-morbidity
factors) influence the length of stay in the neonatal unit.
The comparative method matches infected-cases with
comparable non-infected controls, and is generally the
favored approach.19-21 In order to control for
confounding on total stay and charges, we matched the
cases and controls (control group II) for these factors.
The study found that the extra length of stay was 9.8
days. After the occurrence of the outbreak the difference
was 4 days. Some published studies in neonates
revealed an average extra stay of 24 days,14 6.7 days,22
and 5.2 days.23 The differentiation of results may be
related to several possible reasons. First, in some
studies, neonates were followed until discharge from
NICU14 and in other studies neonates were followed
from the unit.22,23 The neonates of in the present study
were followed until discharged from the hospital.
Secondly, there may be different discharge criteria for
transfer to a low care unit.24 Finally, matching based on
factors associated with infection tends to underestimate
the number of additional hospital stays.20,25 In the
present study, it is believe that our matching criteria
were based on factors associated with duration of
hospitalization. This present study confirms previous
studies by observing that the increase in hospitalization
costs due to nosocomial infection are predominantly
caused by the extension of the duration of
hospitalization.20,23 But in some studies, health care
worker time is the largest proportion of costs.26 The
overall charges for patients with S. typhimurium were
almost 3.5 times those for matched-controls.
Accommodation costs account for more than 44 % of
the total additional charges.
The strain of S. typhimurium that caused the outbreak in
neonatal unit appeared to have been imported from on
local hospital. Such isolates may be multiple antibiotics
resistant and spread rapidly by nosocomial
transmission, particularly in neonatal wards. Rapid
detection and prompt institution of control measures
may limit the outbreak due to such an organism and
prevent systemic infections which are difficult to treat
because of the few antibiotics are available to which the
organism is susceptible. In conclusion, the present
study highlights the importance of outbreak on
healthcare delivery, extra charges and outcomes.
Contributions: Murat Anil, study design, data collection,
statistical analysis, data interpretation, literature search and
manuscript preparation. Mehmet Helvaci, study design, literature
search. Nisel Ozkalay, data interpretation, literature search, and
microbiology studies. Esra Toprak, data collection and literature
search. Ayse berna Anil, Data collection and literature search.
Mustafa Dilek, Data colllection and literature search. Neval
Agus, literature search and microbiological studies.
Conflict of Interest: None
Role of Funding Source: No funding
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