Total Number of Cases that Result in Death
Due to the nature of HABP/VABP, estimation of mortality was quite difficult. As mentioned above, incidence estimates are relatively unrefined because HABP is not a reportable illness, and accurate diagnosis can be complicated. Estimating mortality involves even greater uncertainty due to the fact that HABP occurs in patients who are already hospitalized for other serious conditions, making it difficult to determine whether deaths are due to the underlying illness or HABP/VABP. Accordingly, the mortality rates seen in the literature on HABP/VABP vary widely. As summarized in the 2005 American Thoracic Society/Infectious Diseases Society of America guidelines on hospital-acquired, ventilator-associated, and health care-associated pneumonia, “[t]he crude mortality rate for HAP may be as high as 30 to 70 percent, but many of these critically ill patients with HAP die of their underlying disease rather than pneumonia. The mortality related to HAP (or ‘attributable mortality’) has been estimated to be between 33 and 50 percent in several case-matching studies of VAP.”
In our review of the literature, we saw mortality rates ranging from about 14 percent (Klevens, et al., 2007) to 50 percent (Warren, et al., 2003) to 50 percent and have therefore selected 30 percent as a reasonable middle point among the varying estimates and the low end of the mortality rates reported by the American Thoracic Society/Infectious Diseases Society of America guidelines. Multiplying 30 percent by our estimated number of HABP/VABP cases in 2011, 272,598, results in an estimated 81,779 deaths in 2011.
Due to the difficulties associated with measuring mortality and HABP’s status as a non-reportable illness, we were unable to find a breakdown of deaths by age group. Therefore, to calculate years of life lost, we multiplied the number of deaths due to HABP/VABP by average years of life remaining for the age group including the average age of HABP/VABP patients. We estimated average age by taking the midpoint of the average patient ages reported in two studies, 61.7 (Rello, et al., 2002) and 58.3 (Kollef, et al., 2006), to get 60. Life expectancies by age are available from the NVSR. For a 60-year-old, there are estimated to be 22.6 years of life remaining; thus, each person who died from HABP/VABP is assumed to have lost 22.6 years of life. Multiplying the number of deaths (81,779) by this average life expectancy yields a total of 1,848,212 QALYs lost, due to HABP/VABP deaths in 2011.
To calculate VSL-based mortality costs, we multiplied the number of deaths in each age group by the VSL for those age groups; however, as mentioned above, the literature and available data resources did not provide a breakdown of deaths by age group for HABP/VABP. Therefore, it was necessary to use the VSL for a representative patient (based on average age, which is 60), and multiply that by the annual number of deaths. The VSL for people aged 55 to 62 is $4.77 million.