When a novel virus (novel means a new virus or new strain of virus to which the population would not be expected to have preexisting immunity, and little, if any, cross-immunity [i.e., immunity to other strains of viruses that might be similar enough to provide some protection against the new strain based upon prior infection or immunization against the prior strain]) emerges in a human population and is sufficiently virulent so as to make individuals uncomfortably sick or severely ill, patients will present to emergency rooms and some will be admitted to the hospital, oftentimes, hours or days before the infecting pathogen is identified.
If the virus is efficiently transmissible and health care workers and organizations have not taken appropriate steps (personal protective equipment [PPE] and air handling), those health care workers, staff, patients and visitors within sufficient proximity to the infected patient may be infected. This is a common problem in third-world countries when outbreaks first occur, and unfortunately, it is not unusual for some nurses and doctors to become severely ill or even die.
In 2014, a patient presented to a Dallas emergency room following international travel with a disease we fortunately do not see in the U.S., except in international travelers, almost always those arriving from an African country. Unfortunately, this patient had an infection with Ebola virus that more often than not results in death. Fortunately, it is not among the most transmissible of viruses that we deal with.
Nevertheless, to understand the potential public health threat of this one patient becoming ill in the U.S., 48 individuals had close contact with him after he became ill, but before he presented to the hospital, and another 76 hospital workers cared for him after he presented to the hospital. Two nurses ended up becoming infected, and of course, there were many health care workers who then were required to care for these two new patients. Thus, one can see how a single infected person could expose hundreds of people directly, and then this can be amplified through other people who have subsequently been infected. This is one way in which disease outbreaks can occur, and, under the right circumstances, an outbreak could lead to an epidemic, or rarely, even a pandemic.
The patient with Ebola unfortunately died from his disease. Fortunately, both nurses recovered.
In Wuhan, China, patients began to be admitted to the hospital in December 2019 with an illness that resembled severe acute respiratory syndrome (SARS), which had created an epidemic in 2002 – 2003, but not with the same virus that had caused these new cases of disease. It would subsequently be determined in early January that this new disease outbreak was being caused by a novel coronavirus, which would subsequently be named SARS-C0V-2 to distinguish it from the SARS-CoV that had caused the 2002 – 2003 disease outbreak. Unfortunately, 3,387 health care workers in China had been infected as of February 24, 2020. Many of them no doubt were infected in caring for patients, however, some number of them likely were infected by colleagues or even outside of the hospital with the emergence of community spread of disease. In the U.S., as well, even with our advance notice of this emerging novel viral pandemic, many health care workers were infected while caring for patients, in some cases due to shortages of PPE, but also from family members, children and other close contacts.
In many ways, we have been fortunate that, in the case of the Ebola exposure in Texas, most of those who were exposed did not become infected, and that in the case of SARS-CoV-2, the case fatality rate was not higher. Nevertheless, both examples demonstrate how quickly a novel virus could spread if highly transmissible, given the number of contacts a sick patient is likely to have, and the multiplier effect that would occur if the infectivity (the proportion of those exposed who will develop infection) was very high.
We know that hospital-based spread of infection was an important factor in both prior novel coronavirus disease outbreaks – SARS-CoV in 2003 (Cooper, B. S. et al. Transmission of SARS in three Chinese hospitals. Trop. Med. Int. Health 14, 71–78 (2009)) and Middle East Respiratory Syndrome coronavirus – MERS-CoV in 2012 (Cowling, B. J. et al. Preliminary epidemiological assessment of MERS-CoV outbreak in South Korea, May to June 2015. Euro Surveill. 20, 7–13 (2015). In the case of SARS, the study of three Chinese hospitals demonstrated that transmission rates were higher within hospitals than within communities. In the case of MERS, in a Korean outbreak of the disease, 75 – 89% of infections could be traced to three nosocomial (within hospital) super-spreading events.
A study published last month (The burden and dynamics of hospital-acquired SARS-CoV-2 in England | Nature) attempted to study the burden (amount of disease) and transmission dynamics (how the virus spread) of SARS-CoV-2 within a hospital in England. They examined data from 356 hospitals (excluding children’s hospitals). The differentiation between patients who were infected in the community versus those who acquired the infection following hospitalization was determined on the basis of the interval from the time of hospital admission to confirmed PCR testing for SARS-CoV-2 infection. Community-onset infections were defined as those with an interval of 2 d or less; an interval of 3–7 d led to a classification of indeterminate healthcare-associated; those with intervals of 8–14 d were classified as probable healthcare-associated; and those with intervals of 15 d or more were classified as definite healthcare-associated.
This is not merely an issue of academic interest. Widespread transmission of a virus within hospital can impact the public’s health in many ways. The most obvious is that when health care workers are exposed, they may need to be removed from the workforce temporarily in quarantine, even if not ill. Obviously, if those health care workers become ill, they need to be in isolation and also are unavailable to care for patients, at a time when we already have many shortages of health care workers.
Health care workers in quarantine or isolation may, in turn, inadvertently infect household members or close contacts, which can further contribute to spread of the virus in the community and burden hospitals with more infected patients.
Shortages of health care workers then mean increased expenses for hospitals to pay over-time and, if the shortages are severe enough, significant increased costs to hire temporary replacement staff. Overtime work, temporary staff who are working in a hospital that they are new to and perhaps in an area of care that they are less experienced can result in quality-of-care issues. Further concerns for patient safety and quality of care occur when health care shortages are severe enough or the number of patients being admitted are so high as to result in staff being pulled to care for patients from areas where they don’t deal with these kinds of patients on a regular basis or when patients must be overflowed into areas where these types of patients are not normally cared for.
Further, because patients admitted to the hospital for reasons other than the disease outbreak tend to be very young or elderly and/or immunocompromised, patients who become infected while in the hospital (nosocomial infections) tend to have much higher rates of serious disease and mortality than seen in the general population.
The researchers in the study referenced above estimated that between June 2020 and March 2021 between 95,000 and 167,000 inpatients acquired SARS-CoV-2 in hospitals (definite or probable) in England (1% to 2% of all hospital admissions in this period). Further, the evidence demonstrated that patients who themselves acquired SARS-CoV-2 infection in hospital were the main sources of transmission to other patients. Health care workers, on the other hand, were as likely to be infected by fellow health care workers as patients. Once vaccinated, the rate of infection among health care workers dramatically reduced.
All of this demonstrates the importance of early identification and prompt initiation of infection control measures for patients with new hospital-acquired infections and for other patients they may have infected. Further, these studies reinforce the need for measures that reduce transmission from patients with asymptomatic infection in non-COVID-19 hospital areas, including improved ventilation, use of face coverings by patients and staff, increased distancing between beds, minimizing patient movements within and between patient care units and promotion of hand hygiene. The findings also support efforts to prioritize health care workers (HCWs) for COVID-19 vaccination both due to direct protection to HCWs and due to indirect protection offered to patients. Finally, the findings highlight the need to prioritize research into effective methods of reducing hospital transmission of airborne pathogens for which evidence is currently mounting, including patient care unit design and air filtration systems.
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