Incidence of bacteraemia in a neurocritical care unit

Introduction

The incidence of bacteraemia and bloodstream infection, as defined by the CDC, in our neurosciences critical care unit (NCCU) is at the moment unknown. It is known that being a patient in the intensive care environment is in itself a risk factor for the development of bacteraemia (3.2–4.1 per 100 admissions in several papers). The higher amount of invasive procedures and the severity of illness in this group of patients have been blamed. The aims of our study are: (1) to identify the incidence of bacteraemia in the NCCU, (2) to recognise the incidence of bloodstream infection (SIRS with bacteraemia), (3) to identify the most common pathogens associated with bacteraemia, and (4) to promote the continuous collection of data aiming to follow the behaviour of this problem in time.

Methods

This is a prospective observational study looking at the presence of positive blood cultures in all the patients admitted to the NCCU during the period from 1 June to 31 August 2006. Blood cultures were taken from a peripheral site under aseptic conditions as per the NCCU guidelines. We tried to identify how many of the patients with positive blood cultures had evidence of concomitant SIRS/sepsis, as described by the modified Bone criteria, and the severity of this. An attempt was made to identify the most frequent microorganisms involved in this problem as well as their antibiotic susceptibility. As a secondary aim of our study we described the number of fatalities in the patients with bacteraemia. We tried to focus our approach to the fact that we serve a large neurological/surgical population as well as general patients and to see whether we could pinpoint differences in these two groups.

Results

There were 201 patients admitted to the unit during the period of our study; 140 of these were neurosciences (NS) patients and the rest (61) were general (G) (either medical or surgical). Most of the patients were men and had a mean APACHE II score of 39 (NS group 33, G group 45).There were in total 64 episodes of positive blood cultures (BC); 39 of these episodes were accompanied by inflammatory signs (incidence of bloodstream infections of 19.4% of total admissions). Twenty-five of the episodes were not associated to clinical signs of infection. There were more patients with at least one episode of positive BC in the NS group (29 (20.7%)) than in the G group (10 (16.39%)). Out of 49 episodes in the NS group, 59.18% (29) were associated to some degree of inflammatory response (SIRS, severe sepsis, and MODS). Out of 15 episodes in the G group, 66.6% (10) developed inflammatory response. In 59% (25) of the positive BCs, the organism isolated was coagulase-negative staphylococcus (CNS). In the G group, 47% (7) grew CNS, 33% were diverse Gram-negatives and in 20% other Gram-positives. In the NS group, 64% (31) of isolates grew CNS, 21% were other Gram-positives and 15% were Gram-negatives. In 47 (73.4%) episodes of positive BC, the patients had either a central venous catheter or an arterial catheter. In 36 (56.2%) of the episodes the patients were already on antibiotics at the time of the sampling. The most frequent agent isolated was coagulase-negative Staphylococcus aureus, in 39 (59%) of the cases.

From the patients that had at least one positive BC, nine died; seven (78%) patients were in the G group, and two (22%) in the NS group. Twenty-five (68%) patients with at least one episode of positive BC had a systemic inflammatory response at the time of sampling. Seven (28%) of these died during the first 30 days in the NCCU. Nine (23%) patients had severe sepsis and four (44%) of these died. Four (10.2%) patients had MODS and three (75%) of these died.

Conclusion

We had an incidence of positive blood cultures of almost 32% of the total admissions; 19.4% of admissions developed bloodstream infections. These numbers are very high if we consider the published data. Due to the specialist origin of our unit, we had more cases in the neurosciences group than in the general group. However, the incidence of sepsis and MOF in these patients was almost the same for both groups. We noted, as well, a larger number of deaths in the patients with sepsis and MOF. There needs to be more studies aiming to establish a casual relationship to explain this. CNS was the most frequently isolated organism and there was no difference among the groups. There is a potential for increased mortality in the patients that develop bloodstream infections in our unit, and we need to implement urgent measures to decrease them while further research is done in this area.