Risk of occupational infection with blood-borne pathogens in operating and delivery room settings

Louise J. Short, MD, MSc David M. Bell, MD Atlanta,

Georgia

Surveillance data and case reports substantiate that health care workers are at risk for occupationally acquired infection with blood-borne pathogens. The risk of transmission of blood-borne pathogens to a health care worker depends on the prevalence of blood-borne pathogen infection among patients, the likelihood of transmission of infection per blood contact, and the nature and frequency of occupational blood contacts. In surgical and obstetrical settings, blood contact varies with occupation, specialty, procedures performed, and precautions used. Many contacts appear to be preventable by changes in technique or instrument design and by use of protective barriers. Studies are needed to assess the impact of such interventions. (AJIC AM J INFECT CONTROL 1993;21:343-50)

Several types of studies provide information on occupational infection with blood-borne pathogens (BBPs) in operating and delivery room settings. Surveillance data are useful in assessing the number of health care workers (HCWs) reported to have acquired BBP infections on the job. Three of the primary determinants of the risk of transmission of BBP from patients to HCWs are the prevalence of infection in the patient population, the likelihood of acquiring infection after a single blood contact from an infected patient, and the nature and frequency of blood contact. These factors have been assessed by seroprevalence studies that estimate the prevalence of a BBP in selected patient populations; prospective studies of HCWs after occupational exposure to BBPs to assess risk of infection transmission after a documented exposure; and observational studies and self-administered questionnaires that assess the frequency of occupational contact with blood and other body fluids. In addition, seroprevalence studies of HCWs can be used to estimate BBP From the HIV Infections Branch, Hospital National Center for Infectious Diseases, Control and Prevention, Atlanta, Georgia.

Infections Program, Centers for Disease

Reprint requests: Louise J. Short, MD, MSc, Centers for Disease Control and Prevention, 1600 Clifton Road, Mailstop A-07, Atlanta, GA 30333. 17/o/51064

infection rates in HCWs, serving indirect measurement of risk.

as another

HEP#mls B nfws (HBV) SuwdHamx~ du?a HCWs who lack immunity (e.g., those who have not been vaccinated or have not had previous infection) continue to have a significant risk of occupationally acquired HBV infection. On the basis of sentinel surveillance data, the Centers for Disease Control and Prevention (CDC) has estimated that 5 100 “high-risk” HCWs (those reporting frequent blood contacts) developed occupationally acquired HBV infection in the United States in 199 1. On the basis of knowledge of the natural history of HBV infection, it is estimated that of these 5 100 HCWs, 5% (255) would require hospitalization and 0.1% (5) would die of fulminant hepatic failure. In addition, 10% (5 10) would become chronic carriers, and of these approximately 2 1% (107) would eventually die of cirrhosis or hepatocellular carcinoma (Alter M, CDC, personal communication). Risk

data

Seroprmlence among patients. The risk of HBV infection in HCWs is directly related to the prevalence of HBV infection in the patient population. The prevalence of hepatitis B surface antigenemia is influenced by several factors, in343

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Table

December 1993

1. HBV and HCV seroprevalence

First author Tokars Panlilio

Surgical speclaity

Year 1990 1992

Orthopedics General surgery Orthopedics Gynecology

teZ& 3239 770

studies among

surgeons

% HBV infection (past or current)

% Reporting

13 17

65t 55*

vaccination

% HBV susceptible*

% Anti-HCV poslttve

22

0.8

225

0.9

*Susceptible HCWs were seronegative for hepatitis B core antigen, hepatitis B surface antigen, and antibodies to hepatitis tNumber of doses received unknown, tReported receiving at least three doses. §Cf the total number tested, 8% (62) reported receiving at least one dose of vaccine and had pattern of markers indicating

eluding injectable persons. lence in patients

ethnic group, country of origin, use of drugs, and sexual contact with infected Hepatitis B surface antigen seroprevahospitalized and emergency department has been in the range of 0.9% to 6%.lT4

Risk of acquiring

infection after a blood contact.

For an individual susceptible to HBV, the risk of acquiring HBV infection from a sharp object injury depends on the e antigen status of the source patient (e antigen-positivity correlates with an increased degree of infectiousness). The risk of acquiring infection from a single percutaneous exposure to blood from an e antigen-positive patient is approximately 30%.5-7 The risk of transmission of HBV from a mucocutaneous exposure to blood has not been well quantified but is thought to be lower than that from a percutaneous injury. Seroprevalence among HCWs. Several studies have shown the prevalence of HBV infection to be higher among HCWs than among the general U.S. population. In serosurveys conducted in the 1970s and 1980s the prevalence of HBV infection ranged from 10% to 28% among surgeons’, 9 and from 13% to 49% among anesthesiologists.‘0 In comparison, the prevalence of infection in the general population is 3% to 14%.” New seroprevalence data collected among surgeons since licensure of HBV vaccine are summarized in Table 1. At the annual meeting of the American Academy of Orthopedic Surgeons in 1990, a total of 3239 orthopedic surgeons without nonoccupational risk factors for HIV infection (similar to risk factors for HBV infection but not including ethnic group) were tested. Of these, 13% had serologic evidence of past or current HBV infection, 64% reported having received HBV vaccine, and 22% were susceptible to infection. Age was inversely related to vaccination; 90% of those 20 to 29 years of age and 35% of those older than 60 years reported vaccination.‘* Of 770 hospital-based surgeons in general sur-

B surface

Reference 12 13

antigen,

susceptibility

to HBV infection,

get-y, gynecology, and orthopedics who were tested in a 1992 serosurvey in 2 1 hospitals, 17% had evidence of past or current HBV infection, 55% reported receiving at least three doses of hepatitis B vaccine, and 22% had serologic profiles consistent with susceptibility to HBV infection. This last group included 62 surgeons who reported receiving at least one dose of vaccine but either were nonresponders or had antibody levels that could not be detected.i3 HEPATITIS C VIRUS (HCV) Risk data Seroprevalence among patients.

HCV is a BBP that causes approximately 82% of the cases of non-A, non-B hepatitis in the United States.14 There are no reliable estimates of the number of cases of occupationally acquired hepatitis C in this country. First-generation tests for antibody to HCV became commercially available in 1990, and in 1992 improved assays were released to detect serologic markers for HCV infection. The limited data that have been collected in the past few years reveal that HCV seropositivity varies widely among different patient populations. In a study performed in Baltimore, the investigators tested all adult patients who sought treatment at an urban emergency department during a 6-week period. Of 2523 patients tested, 18% were HCV seropositive.’ A Toronto study that included 3000 patients admitted to a teaching hospital with busy obstetrical, medical, and surgical services found an anti-HCV prevalence of 0.5%.15 Investigators in Germany performed a serosurvey of patients at high risk for HCV infection and found rates of seropositivity to be 86% (24/28) in patients with hemophilia, 63% (32/51) in injection drug users, 28% (1 l/39) in homosexual men, and 9% (2/22) in patients undergoing hemodialysis.16 Risk of acquiring infection after a blood contact. In two studies from Japan, the risk of HCV trans-

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Table 2. HCWs.7with documented and possible occupationally acquired AIDS or HIV infection, by occupation, through June 1993, United Statesz3 Dottrsnr-

Occupstlon Dental worker, including dentist Embalmer/morgue technician Emergency medical technician/paramedic Health aide/attendant Housekeeper/maintenance worker Laboratory technician, clinical Laboratory technician, nonclinical Nurse Physician, nonsurgical Physician, surgical Respiratory therapist Technician, dialysis Technician, surgical Technician/therapist, other than those Other health care occupations

occupattonal (Na.) 1 1 15 1 13 5 1 1 1

listed

above

39

TOTAL

6 3 8 9 6 14 1 15 8 2 2 1 1 3 2 81

l HCWs are defined as those persons, including students and trainees, who have worked in a health care, clinical, or HIV laboratory setting at any time since i 978. fHCWs who had documented HIV seroconversion after occupational exposure: 34 had percutaneous exposures, four had mucocutaneous exposures, and one had both percutaneous and mucocutaneous exposures. Thirty-six exposures were to blood from an HIV-infected person, one to visibly bloody fluid, one to an unspecified fluid, and one to concentrated virus in a laboratory. Eleven of these HCWs have developed AIDS. *These HCWs have been investigated and are without identifiable behavioral or transfusion risks: each reported percutaneous or mucocutaneous occupational exposures to blood or body fluids or to laboratory solutions containing HIV, but HIV seroconversion specifically resulting from an occupational exposure was not documented.

mission after a single percutaneous injury from an infected source patient was 2.7% and lo%, respectively.“-19 Seroprevalence among HCWs. In two serosurveys among surgical personnel conducted by Tokars and coworkers” and Panlilio and associates,13 seroprevalence of antibody to HCV in surgeons was 0.8% and 0.9%, respectively. A study performed in New York City found the prevalence of anti-HCV to be 9.3% among 43 oral surgeons, 0.97% among 4 13 other dentists, and 0.14% among 723 control volunteer blood donors.20 Other studies of anti-HCV in blood donors in the United States have found prevalence rates ranging from 0.3% to 1 .4%.2’* 22 These studies suggest that more data are needed to better define the occupational risk of HCV transmission, particularly among surgical personnel. HUMAN IMIYIUNODEFBCENCY Survelllamce data

As of ports of mented infection umented negative

VIRUS (HIV)

September 1993, CDC had received re120 HCWs in the United States with docuor possible occupationally acquired HIV (Table 2).23 Thirty-nine HCWs had dococcupational exposures, with a baseline HIV test and a subsequent seroconver-

sion. Of these 39 HCWs, 34 sustained percutaneous exposures, four had mucocutaneous exposures, and one had both a percutaneous and a mucocutaneous exposure. Thirty-six exposures were to blood from an HIV-infected patient, one was to visibly bloody fluid from an HIV-infected patient, one was to an unspecified fluid, and one was to concentrated virus in a laboratory. As of September 1993, 11 of the patients with documented seroconversion had a diagnosis of AIDS. Among the 39 HCWs with documented seroconversion is one surgical technician injured with a hollow-bore needle. There has been one documented case of a seroconversion related to an injury with a scalpel contaminated with HIV infected blood (Ciesielski C, CDC, personal communication). For the remaining 81 workers (who are in the “possible” category) the time or source of infection was undocumented. For example, in some cases no baseline serum sample was available and it therefore could not be determined whether seroconversion occurred before or after the exposure. However, none of these HCWs reported behavioral or blood transfusion risk factors and all reported occupational exposures to blood, body fluids, or laboratory solutions containing HIV.

346

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December

Included in the “possible” category are one surgical technician and two surgeons. It is important to recognize that the CDC surveillance system for occupational seroconversions to HIV is passive and cannot be viewed as complete. It is based on reports to CDC by local and state health departments. For the state or local health department to be notified of and confirm an occupational seroconversion, several steps must occur. These include reporting of the exposure by the HCW; medical follow-up documenting seroconversion; reporting of the seroconversion to the health department by the HCW’s physician or other health care provider or by the HCW himself or herself; and obtaining consent from the HCW to participate in interviews with the state or local HIV/AIDS surveillance staff and to allow access to his or her medical and employment records. Underreporting may have a significant impact on our understanding of the epidemiology of exposures. Studies in health care settings suggest that 40% to 90% of percutaneous injuries are not reported. 24, 25 There may also be wide variation in reporting rates among different institutions and occupational groups. It has been speculated that reporting among surgeons may be lower than among other physician groups, and at least one study has found that surgical residents have lower rates of reporting than do medical residents.26 Risk data Seroprevalence

among patients. In the United States, there is wide variation in the rates of HIV seroprevalence among patients. Several studies have estimated HIV seroprevalence in patient populations, CDC’s Sentinel Hospital Surveillance System tested 195,829 anonymous patient specimens at 20 hospitals in 15 cities between September 1989 and October 1991. Patient seroprevalence ranged from 0.2% to approximately 14%.27 A blinded serosurvey of emergency department patients from three suburban and three inner-city hospitals in areas of high AIDS prevalence revealed HIV seroprevalence ranging from 0.2% to 8.9%.28 HIV seroprevalence rates among childbearing women have been reported to range from 0% to 5.8%, with highest rates in certain urban areas.29”1 Risk of acquiring

infection after a blood contact.

All of the documented seroconversions from percutaneous exposures to date have occurred after an injury with hollow-bore needles or other sharp objects including a lance& glass, and a scalpel. None have been documented after injury with

AJIC 1993

solid suture needles. Laboratory studies have suggested that more blood is transferred by deeper injuries and by hollow-bore needles (especially those of larger gauges) compared with solid needles.32* 33 In a study using a porcine skin model, passage of the needle through glove material and decontamination of the wound also reduced the amount of blood transferred by a percutaneous injury. The authors concluded, however, that the HIV titer in the source patient’s blood or other fluid may be the best predictor of the risk of HIV tramsission via percutaneous injury.32 Prospective surveillance of several thousand HCWs after percutaneous exposure to HIV-infected blood indicates that the risk of seroconversion from such an exposure is approximately 0.3%.34”6 This rate is an average of different types of percutaneous exposures from source patients in different stages of HIV disease. In CDC’s surveillance project from August 1983 through June 1992,8 1% of the source patients had AIDS and at least 70% of the percutaneous exposures involved hollow-bore needles.35 Transmission of HIV after mucous membrane and skin exposures has been reported (Table 2). 37 Data from 2 1 studies worldwide include one seroconversion among 1107 mucous membrane exposures (0.09%; 95% confidence interval 0.006% to 0.50%);36 this worker sustained mouth, eye, and hand contact with a large amount of blood from an asymptomatic HIV-positive patient. The risk after isolated skin exposure to HIV-infected blood is believed to be lower but has not been well quantified because no HCWs in prospective studies have seroconverted after such exposures.37 Although inhalation of particles of aerosolized blood (particles less than 100 Frn in diameter, which, unlike droplets, may remain suspended in air for extended periods) may pose a theoretical risk of BBP transmission, no case of such transmission has been documented. The “size” (effective aerodynamic diameter) of an airborne particle containing a BBP depends on the fluid in which the BBP is suspended and the mechanism of. generation of the aerosol; it is always larger than the size of the microorganism itself. Transmission of BBPs by aerosol would require the generation of aerosolized particles of blood, the presence of infective BBPs in these aerosolized particles, and the deposition of a sufficient number of infective blood particles in the respiratory tract or on the mucous membranes of a susceptible host to cause infection. Although it is known that

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347

3. HIV seroprevalence among surgeons No. poslthre

First author

Year

Tokars Panlilio

1990 1992

Surgkal subspc&lly

No. tested

Total

Excluding known risks (%)

Reference

3420 770

2 1

0 (0) 1 (0.14)

42 13

Orthopedics General surgery Orthopedics Gynecology

BBPs can be transmitted through mucous membrane exposure, biologic or epidemiologic evidence that BBPs can be transmitted by aerosols by the respiratory route does not currently exist. Aerosols of blood require considerable mechanical energy to generate (e.g., power equipment) and are unlikely to be present in most clinical settings. It is uncertain whether surgical power tools can generate aerosols containing infective BBPs in clinical situations. Hepatitis B surface antigen could not be detected in the air of dental operating areas during treatment of HBV carriers, including during procedures known to generate aerosols.38 Hemoglobin was detected in aerosols collected from the breathing zone outside of the surgical mask of surgeons during certain procedures39; however, hemoglobin molecules cannot be considered a reliable surrogate for particles containing infective BBPs. In a laboratory study that used blood to which HIV had been added, certain surgical power instruments produced aerosols that in some instances contained infective HIV.40 The clinical significance of this experiment is unclear. HIV serosurveys of surgeons and dentists do not suggest a risk of HIV transmission by aerosol (Table 3).41, 42 For example, in one serosurvey 120 1 orthopedic surgeons without nonoccupational risk factors reported having participated in procedures on patients with HIV infection or AIDS without ever having used a helmet and selfcontained air supply (“space suit”) or other device to prevent inhalation of aerosols. Although the proportion of these procedures in which power instruments were used was unknown, power instruments are used frequently in orthopedic procedures and many of the study participants may have been exposed to blood or tissue aerosols produced by these instruments. All of these 1201 surgeons were HIV seronegative.42 In summary, although further study of the issue is warranted, there are currently insufficient data to support the hypotheses that aerosolized parti-

cles containing infective BBPs may be produced in clinical settings or that BBPs may be transmissible by aerosols in a clinical setting. Seroprevalence among HCWs. Table 3 represents data from two recent HIV serosurveys of surgeons. In the first, two of 3420 orthopedic surgeons were HIV positive; both reported nonoccupational risk factors.42 In the second, one of 770 surgeons in three specialties was HIV positive. This person reported no risk factor other than occupational exposure to HIV, was a general surgeon in practice for at least 2.5 years, had performed at least 300 operating room procedures in the past year, and reported three percutaneous injuries involving patients with HIV infection or AIDS since 1978.13

To prevent occupational blood contacts, knowledge is needed of their circumstances and mechanisms. To determine the frequency and preventability of blood contacts in surgical and obstetrical settings, CDC and others have conducted prospective studies in which HCWs were observed while performing procedures. Several of these observational studies, summarized in Table 4, have assessed the percentage of procedures during which one or more members of the surgical or obstetrical team sustained percutaneous, mucous membrane, or skin contacts.4’ The percentage of procedures with at least one blood contact of any type ranged from 6% in a study in San Francisco to 50% in a study in Milwaukee. The percentage of procedures with at least one sharp injury also varied widely, from 1 .O% to 15%. These variations may be related to differences in study methods, types of procedures observed, and the use of precautions by the surgical team.43-48 In the largest study reported to date to identify risk factors for blood contact during surgery, Tokars and colleagues46 observed 13 82 operations in five surgical specialties (orthopedics, general surgery, gynecology, trauma, and cardiac) in four

348

Table

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4. Prospective

First author Gerberding Panlilio Tokars Popejoy Quebbeman Rudnick *Includes Wdnick

AJIC December 1993

and Bell observational

Location San Francisco Atlanta Surgery Obstetrics New York, Chicago Albuquerque Milwaukee New York Obstetrics

endoscopic procedures and procedures J, CDC, unpublished data.

studies of blood contact No. procedures

among

operating

and delivery room personnel

% Procedures with 2 1 percutaneous Wry

% of procedures with rl blood contact

Reference

1307*

1

6

43

206 230* 1382 684* 234 845

5 2 7 3 15 1

30 32 47 28 50 28

44 45 46 47 48 t

not involving

incision.

hospitals (two urban and two suburban) in areas of high AIDS incidence in the United States. At least one percutaneous injury occurred during 6.9% of these procedures (total 99 injuries). The rate of percutaneous injury varied by occupation. Resident and attending surgeons had the highest rates (2.5 and 2.1 per 100 person procedures, respectively) and circulating nurses had the lowest (none). Percutaneous injury rates also varied by surgical subspecialty. The highest rate was observed in gynecology, in which 10% of procedures were associated with at least one percutaneous injury. Rates also varied by procedure. In a logistic regression analysis, use of fingers to hold tissue while suturing was a risk factor for percutaneous injury. Of percutaneous injuries sustained by surgeons, 62% involved the nondominant index finger. These data suggest that preventive measures such as changes in technique and the development of new devices such as thimbles, blunted suture needles, and punctureresistant gloves may be helpful in the effort to reduce percutaneous injuries. CDC is currently performing a three-part study to assess frequency of blood contacts and evaluate preventive interventions during obstetrical deliveries and gynecologic operative procedures. The study is being conducted in three urban teaching hospitals in cities with high AIDS incidence. In the first phase of the study, 845 deliveries (664 vaginal and 181 cesarean) were observed. During 28% of deliveries, one or more blood contacts (total 276) were sustained, most of which were skin contacts. During 1% of deliveries, one or more percutaneous injuries (total 11) were observed. The largest percentage of the 265 mucous membrane and skin contacts involved the hands (43%) and the forearms (42%). Six percent were

associated with the face; 2% involved the eyes. (Rudnick J, CDC, unpublished data). The second phase of this study involves observation of blood contacts during gynecologic procedures. The third phase assesses introduction of interventions aimed at reducing exposures in operating and delivery rooms. These interventions include technique changes, new devices, and educational programs. Data from the gynecologic observational phase of the study (March to August 1993) showed that gynecologic personnel sustained one or more percutaneous injuries during 7% (37/541) of procedures (38 total percutaneous injuries), and sustained blood-skin contacts during 4 1% (222/541) of procedures (327 total blood-skin contacts). Of 38 percutaneous injuries, suture needles were involved in 29 (76%); 2 1% occurred while the injured person held or steadied tissue while suturing, cutting, or using electrocautery. Thirty-four percent were self-inflicted and 45% were inflicted by a coworker. One percent (18/1416) of double-gloved and 26% (221/858) of single-gloved physicians, medical students, and scrub nurses sustained blood-skin contacts to the hand.49 CONCLUSIONS

The AIDS epidemic has prompted considerable interest in the risk of occupational transmission of all BBPs. HCWs in operating and delivery rooms may sustain contacts with blood and other body fluids. HBV, HIV, and, to a less well understood extent, HCV are the three principal BBPs that currently pose occupational risk to HCWs in the United States. As yet unknown BBPs may also emerge in the future as occupational hazards for HCWs.

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Efforts at reducing the risk of occupational transmission of BBPs in surgical and obstetrical settings should include several components. All surgical personnel should be vaccinated against HBV. The high rate of vaccination among young orthopedic surgeons found in a large HBV serosurvey’* suggests that in several years the HBV infection seroprevalence rates in surgeons will decrease substantially. More studies are needed to define the risk of occupational transmission of HCV. Current evidence suggests that the risk of transmission of HCV through percutaneous injury from an infected patient is higher than that for HIV but much lower than that for HBV. Prevention of blood contacts should be pursued by development of new devices, protective barriers, technique changes, and carefully designed evaluation studies. Further research on postexposure prophylaxis is also needed. Further research will help the surgical, obstetrical, and infectious disease communities pursue strategies for prevention of occupational transmission of BBPs in operating and delivery room settings. Communication and exchange of information at scientific meetings, such as the Conference on Prevention of Blood-borne Pathogens in Surgery and Obstetrics, cosponsored by CDC and the American College of Surgeons in Atlanta in February 1994, will likely stimulate further progress in this area. Thanks to Louis Polish, MD, Mary E. Chamberland, MD, MPH, and Adelisa Panlilio, MD, MPH, for helpful comments on this article, and to Penny McKibben for preparation of the tables.

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O’Neill TM, Abbott AV, Radecki SE. Risk of needlesticks and occupational exposures among residents and medical students. Arch Intern Med 1992; 152: 145 1-6. 27. Janssen RS, St. Louis ME, Satten GA, et al. HIV infection among patients in US acute care hospitals. N Engl J Med 1992;327:445-52. 28. Marcus R, Culver DH, Bell DM, et al. Risk of human immunodeficiency virus infection among emergency department workers. Am J Med 1993;94:363-70. 29. Bell DM, Curran JW. Human immunodeficiency virus infection. In: JV Bennett, PS Brachman, eds. Hospital Infections. Boston: Little, Brown, 1992:823-4&X. 30. Novick LF, Bems D, Stricof R, Stevens R, et al. HIV seroprevalence in newborns in New York State. JAMA 1989;261:1745-50. 3 1. Gwinn M, Pappaioanou M, George JR, et al. Prevalence of HIV infection in childbearing women in the United States. JAMA 1991;265:1704-8. 32. Woolwine J, Mast S, Gerberding JL. Factors influencing needlestick infectivity and decontamination efficacy: an ex vivo model [Abstract 11881. In: Thirty-second Interscience Conference on Antimicrobial Agents and Chemotherapy, Anaheim. Washington, DC: American Society for Microbiology, 1992. 33. Shirazian D, Herzlich BC, Mokhtarian F, et al. Needlestick injury: blood, mononuclear cells, and acquired immunodeficiency syndrome. AM J INFECT CONTROL 1992;20:133-7. 34. Henderson DK, Fahey BJ, Willy M, et al. Risk for occupational transmission of human immunodeficiency virus type I (HIV-l) associated with clinical exposures. Ann Intern Med 1990; 113:740-6. 35. Tokars JI, Marcus R, Culver C, et al. Surveillance of HIV infection and zidovudine use among health care workers after occupational exposure to HIV-infected blood. Ann Intern Med 1993;118:913-9. 36. Ippolito G, Puro V, De Carli G. The risk of occupational human immunodeficiency virus infection in health care workers: Italian multicenter study. Arch Intern Med 1993:153:1451-8.

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Gioanninni P, Sinnicco A, Cariti G. HIV infection acquired by a nurse. Eur J Epidemiol 1988;4: 119-20. 38. Petersen NJ. An assessment of the airborne route in hepatitis B transmission. Ann N Y Acad Sci 1980;353: 15766. 39. Heinsohn P, Jewett DL. Exposure to blood-containing aerosols in the operating room: a preliminary study. Am Ind Hyg Assoc J 1993;54:446-53. 40. Johnson GK, Robinson WS. Human immunodeficiency virus-l (HIV-l) in the vapors of surgical power instruments. J Med Virol 1991;33:47-50. 4 1. Bell DM. Human immunodeficiency virus: transmission in health care settings-risk and risk reduction. Am J Med 1991;91(3B):294.S300S. 42. Tokars JI, Chamberland ME, Schable CA, et al. A survey of occupational blood contact and HIV infection among orthopedic surgeons. JAMA 1992;268:489-94. 43. Gerberding JL, Littell C, Tarkington A, Brown A, Schecter WP. Risk of exposure of surgical personnel to patients’ blood during surgery at San Francisco General Hospital. N Engl J Med 1990;322:1788-93. 44. Panlilio AL, Foy DR. Edwards JR, et al. Blood contacts during surgical procedures. JAMA 1991;265: 1533-7. 45. Panlilio AL, Welch BA, Bell DM, et al. Blood and amniotic fluid contact sustained by obstetric personnel during deliveries. Am J Obstet Gynecol 1992;167:703-8. 46. Tokars JI, Bell DM, Culver DH, et al. Percutaneous injuries during surgical procedures. JAMA 1992;267:2899-904. 47. Popejoy SL, Fry DE. Blood contact and exposure in the operating room. Surg Gynecol Obstet 199 1; 172:480-3. 48. Quebbeman EJ, Telford GL, Hubbard S, et al. Risk of blood contamination and injury to operating room personnel. Ann Surg 1991;214:614-20. 49. Short L, Robert L, Chamberland ME, et al. Frequency and preventability of percutaneous injuries during gynecologic procedures [Abstract 6 181. In: Thirty-third Interscience Conference on Antimicrobial Agents and Chemotherapy, New Orleans. Washington, DC: American Society for Microbiology, 1993.