Epidemiology of candidemia.

A number of studies have identified common riskfactors for patients developing a systemic Candidainfec-tion [9]. Patients that are immunocompromised orimmunosuppressed e.g. because of immunosuppressivetherapeutic regimens or the use of new and aggressive the-rapeutic strategies of life support systems are especially atrisk [10]. These important changes in medical care have tosome extent occurred in all hospitals, but has probablybeen most marked in intensive care units (ICU), in largetertiary care hospitals and in specialized cancer institu-tions. Most of the studies on the epidemiology of candide-mia have been done in single hospitals and the majority ofthese hospitals are probably large, specialized hospitals.The United States and Canada. In an early studyon bacteremia and fungemia from the Boston CityHospital covering seven selected years from 1935 – 1972Candidasp. was not detected in the first three years(1935, 1941, 1947). In the next three years (1953, 1961,1969) the Candidarate remained stable at 3.5% – 3.9% ofmicroorganisms isolated from blood culture, but increasedto 9% in the last year (1972) of the study [11]. Many insti-tutions reported an increase in the occurrence of candide-mia in the mid-1980s. Horn et al. [12] observed that thetotal number of episodes of fungemia increased by 31% inMemorial Sloan-Kettering Cancer Hospital from theperiod 1974-1977 to 1978-1982. A study from HarperHospital showed an increase in the annual incidence ofcandidemia from 23 episodes (4.6% of the total episodesof sepsis) in 1983 to 48 episodes (6.2% of the total) in1986 [13]. There also seems to have been a markedincrease at the Mayo Clinic from the period 1972-1981[14] to the period 1984 – 1992 (Table 1) [15]. At theUniversity of Iowa Hospital and Clinics bloodstreaminfections caused by Candidaspecies increased from2.5% in 1981- 1983 to 7.1% in 1990-1992 [16]. Fraser etal. in a one-year study at Barnes Hospital, St. Louis in1988-1989 found that candidemia patients represented0.33% of total patient discharges and this was a 20-foldincrease in candidemia compared to the years 1976-1979[17]. More comprehensive data from the hospitals partici-pating in the National Nosocomial Infections Surveillancesystem (NNIS) showed a rise in the percentage of all noso-comial bloodstream infections caused by fungi from 5.4%in 1980 to 9.9% in 1990 [18]. During these years the noso-comial fungemia rate increased from 1.0 to 4.9/10,000 dis-charges. Approximately 180 hospitals in the United Statesparticipate in the NNIS system. The hospitals range in sizefrom about 100 beds to more than 1,500 beds [19]. Candidawas the fourth most common nosocomial bloods-tream pathogen among these hospitals [19]. The diagnosis of systemic yeast infections is diffi-cult. It is, however, usually agreed that a positive bloodculture establishes the diagnosis [1,2]. The isolation ofCandidafrom blood is therefore not subject to some ofthe difficulties involved in defining infection as whenyeast is isolated from most other body sites. Blood cultu-res are, however, often negative in patients with systemicyeast infections [3,4]. Nevertheless, if it is assumed thatthe proportion of patients with systemic infection havingcandidemia remains approximately the same over theyears, the number of cases with candidemia serves as animportant marker of the magnitude of this problem. Comparison of data between different hospitals orbetween different time periods in the same hospital is,however, confounded by differences in blood culture met-hodology, in the manner in which data are collected, inthe populations of patients studied etc. Improvements inblood culture methodology may for instance have animportant impact. This is exemplified by the finding inmany studies some years ago that an increase in the volu-me of blood cultured increase the recovery of microorga-nisms [5,6]. Blood culture media has also been improved[7,8]. These changes in methodology have most certainlyincreased the recovery of all microorganisms includingyeasts. Another important problem is that the occurrenceof candidemia is reported in different ways. Usually thetotal number of candidemia cases for a specific timeperiod is given and sometimes also as a percentage of thetotal numbers of patients with bacteremia/fungemia. Ratesare also reported as the total number of candidemia casese.g. per 100,000 population, per 10,000 patient days, per1,000 discharges or per 10,000 admissions to the hospital.All of these reporting methods are quite crude since manyfactors may influence the results. With these reservations in mind it is neverthelessinteresting to compare the occurrence of candidemia andthe distribution of yeast species between hospitals andbetween countries to provide a broad overview of generaltrends and changes. This review compares a number ofstudies from different parts of the world (Tables 1 – 3) inattempt to find an answer to the following questions: a)has the occurrence of candidemia increased? b) Are theredifferences between countries regarding the occurrence ofcandidemia? c) What is the species distribution of