Specific Considerations
Many factors may combine to increase the risk for infection among workers during pathogen transmission. Categories of risk factors for work-related infections include disease factors (such as transmission mode), workplace factors, and worker factors. Considering each of these categories during case investigations is useful in planning and implementing prevention and control strategies.
Disease Factors
Infectious disease can be transmitted via direct contact (including percutaneous), droplet, airborne (aerosol), vehicles (such as food, water, and fomites), and vectors (Table 2). The studies included in our review suggest that occupations involving interaction with the general population, particularly ill persons, pose an increased risk for infection.
As one example, teachers and public service workers may acquire respiratory virus infections, including influenza and measles, because their work may bring them in contact with persons who are ill.[7–10] Workers in the healthcare industry are also at risk for influenza as well as airborne (such as tuberculosis [TB]) and percutaneously transmitted (such as HIV) infection from patients.[11–13] In 2014, work-related Ebola virus infections among healthcare personnel were a substantial component of the Ebola epidemic worldwide; 2 healthcare personnel acquired Ebola virus disease within the United States.[14,15] Occupational contact with human corpses can also result in infectious disease. In 2007, an embalmer in New York, New York, USA, contracted Mycobacterium tuberculosis from a cadaver.[16]
Disease transmission patterns are also relevant to those whose work brings them in contact with animals, putting them at risk for zoonotic infections. Occupational exposure to livestock and poultry contributed substantially to work-related infectious diseases. Twenty-nine cases of Campylobacter infection occurred over a period of several years among workers at a poultry processing plant,[17] and sealpox virus infections were reported among animal rescue workers in a marine mammal rehabilitation center.[18]
Transmission of pathogens in the workplace may occur in 2 directions: workers can acquire infections in the workplace and then also may serve as vectors that spread the disease to others, such as clients and co-workers. We found that workers in food preparation and serving-related occupations have been identified as sources of transmission in foodborne outbreaks. Two delicatessen workers infected with Salmonella from occupational contact with chicken became the source of disease transmission in a 2007 salmonellosis cluster in Minnesota.[19] Transmission of norovirus gastroenteritis among workers and customers at a restaurant has also been reported.[20] These examples show that preventing workers from acquiring infections in workplaces may also prevent disease transmission among the general public.
Pathogens in the environment can also serve as a source of worker infections through the respiratory route. A 2006 report described a 21-year-old healthy landscaper diagnosed with tularemia. Traditionally thought of as a zoonotic pathogen, Francisella tularensis can also be acquired via aerosolized bacteria during occupational activities such as lawn mowing and leaf blowing.[21] Another report described 2 spa maintenance workers infected with Mycobacterium avium complex organisms, which live in water and are highly resistant to disinfectants, such as chlorine. Occupational exposure to aerosolized bacteria during routine cleaning and maintenance of spa filters and tubs was the likely cause of this outbreak.[22]
Workplace Factors
Regardless of transmission mode, workplace factors can contribute to the propagation of infection. It is crucial to identify aspects of the workplace that pose biologic hazards, because those aspects may be amenable to controls. Such factors can include workplace characteristics, work practices and processes, and engineering and administrative issues. For example, work-related fungal respiratory infection is a concern in some areas. Outbreaks of coccidioidomycosis have occurred among construction workers and outdoor film production workers in California;[23,24] during 2011–2014, a total of 44 cases of coccidioidomycosis were identified among workers constructing solar power farms.[25] Outdoor workplaces with hot, dry conditions in areas of endemicity pose a risk for coccidioidomycosis because soil-disruptive activities and high winds expose workers to dust harboring Coccidioides spores. Other factors may also contribute. In 2012, Nebraska officials reported an investigation of a cluster of histoplasmosis among 32 day camp counselors.[26] The probable infection source was campsite contamination of soil and picnic tables by bat guano, which probably became aerosolized during camp activities or cleanup.
Engineering factors can also promote disease transmission in the workplace. Previous studies have shown that workplace environmental characteristics contributed to M. tuberculosistransmission among workers.[27] During the outbreak investigation of TB among workers at an elephant refuge in 2009, investigators found that shared air between the administrative area and the barn, along with pressure-washing of the barn by workers, contributed to transmission.[28] Laboratories are another example of unique workplaces where engineering controls (such as biosafety cabinets and local exhaust ventilation) are essential for reducing or eliminating potential biologic hazards to workers. Laboratory workers have acquired Salmonella infection, vaccinia virus infection, plague, cowpox, brucellosis, meningococcal disease, and HIV infection through accidental direct contact with pathogens in the workplace over the past decade.[13,29–35]
Administrative issues, including workplace policies and practices, can also play an important role in disease transmission in the workplace. In 2014, the California Department of Public Health reported an occupational HIV outbreak among adult film performers.[36] Some adult film production companies rely on HIV testing results as a control and require performers to engage in penetrative sex without a condom. This approach is problematic, because during acute infection, a performer can transmit the infection even when HIV test results are negative. This example highlights that the lack of a protective administrative policy in the workplace could lead to infectious disease transmission among workers.
For workers in high-risk environments, employers have a responsibility to provide adequate prophylaxis for prevention of infectious disease. However, sometimes employers or workers are unfamiliar with or unable to comply with the relevant recommendations. For example, CDC staff found 4 malaria cases among employees of a commercial airline who had all traveled to Ghana and stayed at the same hotel before disease onset. None had used antimalarial chemoprophylaxis provided by the company.[37] It is unclear why they did not use the chemoprophylaxis, but this cluster underscores the importance of a comprehensive malaria prevention program that includes education and counseling.
Worker Factors
Individual characteristics, such as impaired immunity, inadequate prophylaxis, and socioeconomic and language factors, may increase the risk for acquisition and transmission of infectious diseases. For example, a case of fatal laboratory-acquired infection caused by Y. pestis occurred in a laboratorian in 2009.[32] No additional cases or major deficiencies in engineering controls were identified in this laboratory. A postmortem examination revealed that the affected worker had hereditary hemochromatosis, a condition that increases susceptibility to infection with certain bacterial pathogens. In another situation, Campylobacter infection among poultry-processing workers was found to occur most frequently during the first weeks of work, after which the workers develop immunity that may be protective against future infection.[17] Therefore, investigators should consider that individual host susceptibility to certain diseases may play a role in disease transmission in workplaces.
Documented nosocomial transmission puts healthcare personnel at substantial risk for acquiring or transmitting several vaccine-preventable diseases, including hepatitis B, influenza, measles, mumps, rubella, pertussis, and varicella. The Advisory Committee on Immunization Practices and the Hospital Infection Control Practices Advisory Committee recommend that healthcare personnel be vaccinated or have documentation of immunity for all of these diseases; employers must formulate a comprehensive vaccination policy for all healthcare personnel.[38,39] Workers in other settings, such as public services, may also be at risk for exposure to vaccine-preventable diseases, such as measles. In 2007, an airport officer contracted measles from an international traveler and may have transmitted it to a second airport worker.[9] In 201l, a US Customs and Border Protection officer contracted measles after processing an arriving refugee with measles.[10] All of these situations underscore that immunizations should be kept current for workers whose jobs involve frequent contact with the public.
In addition to individual susceptibility and immunity, a worker's socioeconomic status could contribute to risk. Texas officials reported a TB outbreak investigation among workers in a meatpacking plant in 2011. The index case was in a foreign-born patient who had cavitary TB with acid-fast–positive smears. Most of the patient's work contacts were foreign-born. Investigators found that low economic status, limited access to healthcare, and communication and language barriers caused delays in diagnosis and played significant roles in TB transmission among immigrant workers.[40]
Emerging Infectious Diseases. 2019;25(3):397-405. © 2019 Centers for Disease Control and Prevention (CDC)
