The study was supported by a grant from the research project K/ZDS/000649

Ventilator-associated pneumonia (VAP) is one of the commonest nosocomial infections in ITUs. VAP markedly increases morbidity and mortality rates of hospitalized patients and is associated with the highest costs resulting from long hospitalization, pharmacological treatment, etc. The main factors increasing the risk of VAP include age, pregnancy, underlying diseases, past traumas and instrumental therapy (e.g. endotracheal intubation), earlier antimicrobial treatments and long-term immobilization. Moreover, VAP is one of the most important and severe complications in patients undergoing surgical treatment  (high mortality). The risk of pneumonia, including VAP is particularly high in patients after abdominal and thoracic surgeries.

Despite advances in medicine, better surgical techniques and broader knowledge of pathomechanisms of its development, VAP is a serious problem in intensive therapy units, both worldwide and in Poland [1,2,3].

The objective of the present study was epidemiological and microbiological analysis of nosocomial pneumonias, which developed in patients undergoing artificial lung ventilation after cardiac surgery in 2007.

METHODS

The study was carried out in the ITU within the Infection Surveillance System prepared and coordinated by the Polish Society for Hospital Infections together with the Department of Microbiology, Collegium Medicum, Jagiellonian University in Krakow. The hospital infection control team identified the cases of pneumonia in artificially ventilated patients according to the definitions and criteria of the National Healthcare Safety Network (NHSN) [4].

In each case, the material for microbiological examinations was collected to isolate the etiological factors. Antibiotic-sensitivity of bacteria considered the etiological factors of VAP was assessed in accordance with the recommendations of the Clinical and Laboratory Standards Institute (CLSI) [5]. 

The epidemiological conditions of the ITU were described using the following epidemiological measures:

1. cumulative incidence as the number of new VAP cases in the population of patients undergoing surgery (in the present study this number corresponded to the number of surgical procedures) for unit time, i.e. a year, converted into the number of procedures performed over this period,

2. incidence density describing the number of new cases of VAP for unit time in relation to total person-time of ventilation of patients operated on when staying in the ITU, as the method recommended by the Center for Disease Control and Prevention (CDC) for analysis of quality management,

3. mortality  rates (percentage of VAP cases directly or indirectly related to death in the total number of VAP cases),

4. distribution of isolated etiological factors,

5. proportion of extremely resistant species in the total bacterial population.

Infections were registered using the unified questionnaire – the hospital infection chart. Demographic data (age, gender, cause of admission, date of admission, discharge or death) and information about patient`s status, risk factors, surgery, diagnostic and therapeutic procedures, microorganisms recognized as etiological factors and their markers of resistance were colleted for each patient with the symptoms of infection.

The results were assessed using the analysis of incidence density rates of VAP recommended by CDC [6, 7]. The kinds and drug resistances of microorganisms regarded as VAP etiological factors were described in relation to the NHSN data [8]. The statistical tests of likelihood ratio (LR) were used. For the analysis of aetiology of VAP cases, p=0.05 was considered statistically significant.

RESULTS

In 2007, 2420 coronary and other cardiovascular surgeries were performed in the hospital. Thirty-eight pneumonia cases were detected among artificially ventilated patients. Once criteria were assessed in detail, 28 VAP cases were encompassed for analysis: 22 male and 6 female patients, aged 68 years (range 50-80 years). One patient died. The cumulative incidence of VAP was 1.2%, incidence density – 9.6/1000 ventilation days, mortality – 3.6% (Fig. 1). Mechanical lung ventilation in the group examined was carried out for 2902 days. The ventilation utilization ratio (VUR) was 0.52 (number of days of ITU stay: 5620) (Fig. 2).

First symptoms of VAP were observed after 13 days, on average (median 12 days); in 7 (25%) cases the symptoms developed early (<7 days); in the remaining cases – on ventilation day 7 or later. Each patient underwent microbiological tests; in 27 (68%) cases, the material was collected invasively using bronchofiberoscopy. In one cases, the etiological factor was not identified whereas in 17 the multifactor aetiology was demonstrated. In 8 patients, the etiological factor changed at successive examinations (without health periods), in 3 – the “secondary” microorganisms were yeast-like fungi.

In 11 patients, the diagnosis of pneumonia was preceded by symptoms of generalized infection.

The isolated etiological factors were predominantly Gram-negative bacteria, constituting 87.5% of all analysed microorganisms. The most common isolates were Enterobacteriaceae: Klebsiella pneumoniae and Escherichia coli as well as non-fermenting Pseudomonas aeruginosa. Moreover, Enterobacter cloacae, Acinetobacter baumannii and Serratia marcensces were found (6.3% of all isolates, each). Proteus bacteria accounted for 10.4% of isolates (Table 1). The frequency of isolation of various groups of microorganisms was significantly different from the NHSN data (LR=22.548, p=0.0125).

Bacteria producing extended-spectrum β-lactamases (ESBL phenotype) constituted 37.5% of Klebsiella pneumoniae strains. Among Pseudomonas aeruginosa, 60% were found resistant to carbapenems. In the group of Gram-positive cocci, the presence of MRSA was detected, which was also resistant to macrolides, lincosamides, streptogramins B (MLSB) and fluorochinolons; moreover, high-level ampicilin-resistant (HLAR) Enterococcus faecium  was found (Table 2).

DISCUSSION

The presented data concern a highly specialized hospital with cardiac surgery department. Hospital acquired infections have been controlled there since 1998 and the Infection Control System has been used since 2002. The infection control team consists of nurses specialized in epidemiological nursing and a specialist in infectious diseases closely cooperating with diagnostic microbiologists and pharmacologists. Experience and skills of the team are confirmed by the data published earlier concerning incidences of surgical-site infections [9]. The previous analysis of patients concerned the years 2002-2004 and indicated that the incidence of surgical-site infections was about 3%, which is in agreement with the expected values observed in the American NHSN and German Krankenhaus Infektions Surveilance System (KISS).

The present analysis, on the other hand, points out a relevant problem connected with control over other forms of clinical infections dangerous for ITU patients. The epidemiology of VAP in the ward in question differs (incidence density of VAP is significantly higher) from the anticipated or comparative data, e.g. those obtained from NHSN [8, 10]. The incidence described as incidence density of VAP among patients treated with ventilators in American ICUs is 5.7/1000 ventilator days (Fig. 1). The median is 4.0 using the VUR and the average intensity of 41% (Fig. 2). The hospital evaluated in the present study is characterized by higher ventilator utilization rates (52% – corresponding to 75 percentiles of NHSN results), which places the examined unit in the group of 25% of cardiac surgery ITUs most intensively utilizing this form of therapy. 

The epidemiology of VAP is similar; the unit is characterized by the highest prevalence rates of VAP amongst ITUs of similar profiles. Thus, it should be assumed that the epidemiology observed corresponds with high intensity of therapy and burden of treated patients; hence, one of important elements of control of the population examined is higher than expected frequency of mechanical lung ventilation.

The issue of VAP etiological factors is slightly different. In the unit studied, significant differences in the profile of isolated microorganisms were observed. The proportion of Candida albicans is of particular interest as their occurence is 3 times higher compared to NHSN data. This is likely to be related to increased intensity of mechanical lung ventilation applied. Therefore, it is worth considering possible modifications of procedures to carry out or to discontinue this therapy as well as changes in the patients` care and hygiene.

The multi-centre studies highlight that the risk of nosocomial pneumonia is high in critically ill surgical patients; this risk is even higher than that of surgical-site infections [11, 12, 13], particularly in departments of cardiac and thoracic surgery. Our findings are not alarming yet indicate that the infection control team should undertake measures to reduce the risk of VAP (of fungal aetiology, in particular). This is confirmed by the fact that mortality in the population studied is not high (3.6%) whereas in patients with VAP symptoms it may even amount to 30-60% [14].

CONCLUSIONS

1. Increased incidences of VAP correlate with the frequency of mechanical lung ventilation applied.

2. VAP etiological factors are mainly Gram-negative bacteria with some proportion of yeast-like fungi.

3. Drug resistance of isolated microorganisms confirms the necessity for control of this part of ward epidemiology and permanent cooperation of the infection control team, microbiological laboratory and pharmacologists.

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REFERENCES

1.    Wójkowska-Mach J, Bulanda M, Różańska A, Heczko PB: Szpitalne zapalenie płuc w oddziałach intensywnej terapii. Analiza Systemu Czynnej Rejestracji Zakażeń Szpitalnych Polskiego Towarzystwa Zakażeń Szpitalnych. Przegl Epidemiol 2006; 60: 225-235.

2.    Wójkowska-Mach J, Bulanda M, Różańska A: Hospital acquired pneumonia in the intensive care units of Polish hospitals. Infect Control Hosp Epidemiol 2006; 27: 784-786.

3.    Wójkowska-Mach J, Bulanda M, Różańska A, Jawień M, Heczko PB: Nadzór nad zakażeniami w polskich szpitalach w roku 1999 i w latach 2002-2003 na przykładzie szpitalnego zapalenia płuc w oddziałach intensywnej terapii. Anest Inten Terap 2005; 37: 188-192.

4.    Horan TC, Gaynes RP: Surveillance of nosocomial infection. In: Mayhall CG: Hospital epidemiology and infection control. Lippincott Williams & Wilkins, Philadelphia 2004: 1660-1702.

5.    Clinical and Laboratory Standards Institute CLSI: general susceptibility testing. performance standards for antimicrobial susceptibility testing. Eighteenth informational supplement, Wayne, 2008.

6.    Bonten MJ, Koffer MH, Hall JB: Risk factors for ventilator-associated pneumonia: from epidemiology to patient management. Clin Infect Dis 2004; 38: 1141-1149.

7.    Eggiman P, Hugonnet S, Sax H: Ventilator-associated pneumonia: caveats for benchmarking. Intensive Care Med 2003; 29: 2086-2089.

8.    Hidron AI, Edwards JR, Patel J, Horan TC, Siwert DM, Pollock DA, Fridkin SK: Antimicrobial-resistant pathogens associated with healthcare-associated infections: annual summary of data the Center for Disease Control and Prevention, 2006-2007. Infect Control Hosp Epidemiol 2008; 29: 996-1011.

9.    Wójkowska-Mach J, Baran M, Synowiec E, Foryciarz E, Bigosiński J, Sadowski J, Bulanda M, Heczko PB: Nadzór nad zakażeniami miejsca operowanego po zabiegach z zakresu chirurgii serca – doświadczenia własne. Przegl Lek 2008; 65: 7-8.

10.    Edwards JR, Petersom KD, Andrus ML, Telson JS, Goulding JS, Dudek MA, Mincey RB, Pollock DA, Horan TC: National Healthcare Safety Network (NHSN) report, data summary for 2006. Am J Infect Control 2007; 35: 290-301.

11.    Bonten MJ, Koffer MH, Hall JB: Risk factors for ventilator-associated pneumonia: from epidemiology to patient management. Clin Infect Dis 2004; 38: 1141-1149.

12.    Arozullah AM, Khuri SF, Henderson WG, Daley J: Development and validation of a multifactorial risk index for predicting postoperative pneumonia after major noncardiac surgery. Ann Intern Med 2001; 135: 847-857.

13.    Gastmeier P, Geffers C, Brandt C, Zuschneid I, Sohr D, Schwab F, Behnke M, Daschner F, Rüden H: Effectiveness of a nationwide nosocomial infection surveillance system for reducing nosocomial infections. J Hosp Infect 2006; 64: 16-22.

14.    Leu HS: Hospital-acquirade pneumonia. Attributable mortality and morbidity. Am J Epidemiol 1989; 129:1258-1267.

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Address:

*Jadwiga Wójkowska-Mach
Katedra Mikrobiologii Collegium Medicum UJ
31-121 Kraków, ul. Czysta 18
tel. 012 633 00 60, fax. 012 423 39 24
e-mail: mbmach@cyf-kr.edu.pl

Received: 22.07.2009
Accepted: 14.09.2007