From 1999 through 2005, annual hospital discharges in the United States increased ≈8%, from 32.1 million to 34.7 million. During this period, the estimated number of hospitalizations involving S. aureus–related infections increased 62%, from 294,570 (95% CI 257,304–331,836) to 477,927 (95% CI 421,665–534,189). S. aureus–related hospitalizations with diagnosis codes for septicemia and pneumonia increased 38% and 7%, respectively, and hospitalizations involving other S. aureus–related infections in conditions classified elsewhere nearly doubled. Overall, the rate of S. aureus–related diagnoses per 1,000 hospitalizations increased 50%, from 9.17 to 13.79 ().
Staphylococcus aureus and methicillin-resistant S. aureus (MRSA)–related hospital discharge diagnoses, by infection site and year, United States
From 1999 through 2005, estimated MRSA-related hospitalizations more than doubled, from 127,036 (95% CI 112,356–141,716) to 278,203 (95% CI 252,788–303,619). MRSA-related hospitalizations with a diagnosis code for septicemia increased 81.2%, from 31,044 (95% CI 25,170–36,918) to 56,248 (95% CI 46,830–65,665), and MRSA-related hospitalizations with a diagnosis code for pneumonia increased 19.3%, from 30,632 (95% CI 24,597–36,666) to 36,540 (95% CI 29,527–43,554). The largest increase in MRSA-related hospitalizations involved infections outside the lungs or blood; these almost tripled from 65,361 (95% CI 55,801–74,920) to 185,415 (95% CI 162,102–208,728). Overall, the rate of MRSA-related discharges per 1,000 hospitalizations more than doubled, from 3.95 to 8.02 ().
Estimated methicillin-resistant Staphylococcus aureus (MRSA)–related hospitalization rates, United States, 1999–2005. Rates are no. MRSA-related discharges/1,000 hospitalizations. Error bars represent 95% confidence intervals.
In hospitalizations for which S. aureus–related septicemia and pneumonia were listed as any 1 of the 7 discharge diagnoses, these diagnoses were coded as the primary diagnosis, on average, in 38% (standard deviation 6.4%) and 54% (3.7%) of records, respectively, over the 7-year period. The most frequent primary diagnosis associated with other S. aureus–related infections was other cellulitis and abscess (ICD-9 682), followed by postoperative infection (ICD-9 998.59), infections from an implanted device or graft (ICD-9 996), osteomyelitis (ICD-9 730), and diabetes mellitus (ICD-9 250). Cellulitis infections increased >25% per year from 22,451 (95% CI 17,007–27,895) to 87,500 (95% CI 75,485–99,515), which was nearly a 4-fold increase. No other primary diagnosis infection code increased over this time period ().
Figure 2 Primary diagnoses of Staphylococcus aureus–related hospitalizations. The most frequent primary diagnosis associated with other S. aureus–related infections was other cellulitis and abscess (International Classification of Diseases [ICD]-9 (more ...)
Similar rates of discharge associated with S. aureus–related and, more specifically, MRSA-related infections per 1,000 hospitalizations were observed across all 4 US regions (Northeast, South, Midwest, and West; ). Overall, the rate of S. aureus–related infections increased 5% per year in the Northeast, 7% in the Midwest and South, and 8% in the West. The rate of MRSA-related infections in the Northeast, Midwest, and South increased 9%, 11%, and 12% per year, respectively. In contrast, the West had the lowest incidence and frequency of MRSA-related infections, but the rate of MRSA-related infections increased 18% per year. Although increases were considerable, none of the rates in any region was significantly different in any year from the others at the 95% CI level.
Hospitalizations and rates of infections with Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) by region and year, United States*
In 2005, there were ≈11,406 S. aureus–related deaths (95% CI 7,609–15,203), of which 6,639 were MRSA-related (95% CI 4,429–8,850). Since 1999, no trend was seen in the number of deaths. We estimated that S. aureus–related deaths averaged ≈10,800 per year (range 7,440–13,676) and MRSA-related deaths averaged ≈5,500 per year (range 3,809–7,372) (). However, the percentage of S. aureus–related and MRSA-related hospitalizations that resulted in death did show a trend, a decrease from ≈3.7% in 1999 to only 2.4% in 2005. We also calculated the number of deaths in which any diagnosis code was S. aureus–related. These calculations showed that deaths with an S. aureus–related discharge code increased 18% from 24,715 (95% CI 17,853–31,577) to 29,164 (95% CI 21,620–36,708) from 1999 through 2005. Deaths in which MRSA was likely present increased >50%, from 11,240 (95% CI 8,117–14,362) to 17,260 (95% CI 12,794–21,726) over the same period. However, despite the increases, the percentage of S. aureus–related hospitalizations that resulted in death decreased from 8.4% in 1999 to 6.1% in 2005, and the percentage of MRSA-related hospitalizations that resulted in death decreased from 8.8% to 6.2%.
Estimated hospital deaths associated with Staphylococcus aureus and methicillin-resistant S. aureus (MRSA), United States, 1999–2005. Error bars represent 95% confidence intervals.
S. aureus resistance to ampicillin/sulbactam, cephalothin, and erythromycin increased 21%, 35%, and 27%, respectively, during the study period. Resistance to gentamicin and trimethoprim-sulfamethoxazole decreased 76% and 64%, respectively. No instances of vancomycin-resistant (or intermediate-resistant) S. aureus in hospitalized patients were reported.