In this retrospective cohort study involving patients with HAP/VAP in a tertiary teaching hospital in Taiwan, the incidence of HAP was incidence of 0.22 (95% CI, 0.19–0.26) per 1,000 patient-days and that of VAP was 0.27 (95% CI, 0.12–0.53) per 1,000 ventilator-days of use. Overall, our study reported a high all-cause mortality rate and high medical expenditure associated with patients who were complicated with HAP/VAP.
According to the Taiwan nosocomial infection surveillance system (TNIS) system, the burden of VAP was 0.6 per 1,000 ventilator-days in the medical center and 0.9 per 1,000 ventilator-days in the regional hospitals in 2018 [14]. The incidence rate reported in our study was slightly lower than the national surveillance data. Since all cases reported from the automated system was reviewed individually to fit the diagnostic criteria, it is possible that our system might underestimate the incidence HAP/VAP by only selecting those with the most obvious clinical findings and severities. However, the low incidence rate in our study as well as the national surveillance data were still comparable with our prior systemic review, we had demonstrated a statistically significant reduction of HAI incidence from 2008 to 2015 in Taiwan, South Korea and Japan [9]. In Taiwan, the improvement may attributable to the development of TNIS system (available since 2000 and online since 2006), hand hygiene program since 2007, and care bundle program since 2011. The incidence of VAP had 57.7% reduction during the study period in Taiwan. But the incidence of HAP is not available in Taiwan’s national surveillance data. Chawla R, et al had tried to provide the comparison of HAP incidence among 10 Asia countries [8], and they had reported an HAP incidence between 0.51–0.85 per 1000 patient-days in Taiwan in 2008, which was possibly generated through personal communication. To our best knowledge, this is the first article in English provide the disease burden of HAP in Taiwan.
The reported incidence of HAP/VAP also varied greatly in different regions. The NHSN reported an VAP incidence of 1–2.5 cases per 1000 ventilator-days in 2011 in the United States [4]. However, Koulenti and colleagues reported a much higher incidence of 18.3 episodes per 1000 ventilator-day among 27 European ICUs in 2006 [5]. The huge differences among incidence rate might partially explained by the difference of case definition. The case definition used in our hospital surveillance system (and hence in our study) was in line with the definition proposed by the US CDC, while the study by Koulenti et al. was based on clinical judgment and interpretation of culture results. This highlighted the importance of a globally unified definition in order to compare the burden of HAP/VAP in different healthcare settings.
One of the challenges in HAP/VAP is the identification of causative microorganism. In past literatures, clinical cultures, including expectorated sputum, tracheal aspirate and blood, could identify around 50% of the causative pathogen [15]. Since the selection of antibiotics might be impacted by the difficulty in identifying pathogens and might resulted in increased risks of mortality or morbidity, the 2016 treatment guideline published by Infectious Diseases Society of America (IDSA) and the American Thoracic Society (ATS) had suggest each hospital should build-up its own antibiogram to facilitate the optimal choice of antibiotics [16, 17]. In our study, the top five common pathogens in nvHAP and vHAP were Gram-negative bacteria, including Acinecobacter baumanii complex, Pseudomonas aeruginosa, Klbsiella pneumoniae, Escherichia coli, Stenotrophomonas maltophilia and Elizabethkingia species, which was also consistent with the finding in the national surveillance data of VAP in Taiwan [14]. Our results might offer an evidence in choosing optimal empiric antibiotics, and de-escalating should be considered while culture result available.
The all-cause mortality among patients with HAP and VAP in our report was 59.0% and 37.5%, respectively. Furthermore, there was no statistically significant difference in the mortality rate among those with vHAP and nvHAP in our study. However, unlike our observation, Talbot G. et al reported a lower much overall HAP mortality and had observed a slightly lower risk of mortality among those with nvHAP, when compared with patients of vHAP [10]. This difference might be partially explained by the inclusion criteria of different studies. The study from Talbot et al. included data from several drug trials and might had excluded those who were ineligible for clinical studies. Also, as aforementioned, our study might have underestimated the incidence of HAP/VAP and overlooked less severe patients.
In the addition, HAP/VAP also lead to substantial increase of medical expenditure. In a systemic review, Zimlichman E, et al estimated that an episode of VAP would associated with 13.1 additional days of hospital stay (8.4 days in ICU) and surplus expenses of 40,144 USD [18]. According to the NHSN, VAP ranked 2nd for the most overall attributable cost among the major HAI in the United States, following only by surgical site infection (SSI). Wagh H, et al also reported the estimated cost due to VAP was £6000 and £22000 per patient in the United Kingdom (7). According a study using administrative data from Malaysia, Indonesia and Philippines, Azmi S et al. reported the LOS due to HAP ranged from 6.9–10.2 in these countries, and the estimated cost per patient was 784,300-1,882,140 USD [19]. Our study added pieces to the evidence which estimating the cost of HAP/VAP, although the difference related socioeconomic infrastructure had made the comparison difficult.
There are several limitations of this study. Since the data is obtained from a tertiary care hospital, thus the incidence of HAP/VAP and outcome may not be generalized to other hospitals setting with patients with fewer comorbidity and lesser disease severity. Second, our study likely underestimated the incidence of HAP/VAP and warrant careful interpretation when applied. However, our results might still help guiding clinicians dealing with most severe HAP or VAPs.