A Comprehensive Update on SARS-CoV-2 and COVID-19

Part II (continued)

Transmission Characteristics of SARS-CoV-2

This is part of a long blog series to update readers with a complete overview of the SARS-CoV-2 virus and the disease it causes – COVID-19. In Part I, we reviewed in quite some detail the updated understanding of the biology of the SARS-CoV-2 virus. In Part II (the last blog post), we reviewed the transmission characteristics of SARS-CoV-2, including the transmission mode, the incubation period, the serial interval, the latent period and the infectious period. We also covered the many ways we can determine directly or indirectly what the infectious period is – epidemiological observations, inferences from PCR tests as a proxy for viral load or duration of rapid antigen test positivity as an indication of viral shedding, and more complicated methods to measure more directly the infectious period. Because we covered so much ground, I decided to break Part II up into two parts. This is the second part.

III. Nosocomial transmission of COVID-19

Nosocomial infections refer to those that are healthcare-acquired infections, most often in a hospital setting, and meaning that the person did not enter the health care facility with the infection, but acquired the infection during the course of their care for a different problem.

Early on in the pandemic, every patient admitted to the hospital was screened for COVID-19 (recall that initial reports suggested that roughly 40% of infections occurred in persons who were asymptomatic (never developed symptoms), presymptomatic (were not yet symptomatic but would eventually become symptomatic), or pauci-symptomatic (had few and mild symptoms such that they suspected that they were just overly tired or perhaps experiencing allergies as opposed to might have COVID-19), and that in doing so, persons being admitted for other reasons might be found to have COVID-19. Obviously, if these patients test positive upon admission to the hospital, they would not be classified as hospital-acquired infections, but rather community-acquired. Thus, with testing everyone upon admission, we knew each patient’s status as to whether they already had COVID at the time of admission.

Further, back then, and for the most part into 2022, protections were taken by all hospitals to protect staff and patients – usually a combination of mask requirements (though I don’t have the foggiest idea how they read the same studies that I did and thought that procedure masks were sufficient), some program for testing employees, vaccine requirements, isolation of sick employees and quarantine of exposed employees, as well as limits on visitors (though visitation policies often showed wide-ranging differences between different hospitals and internal inconsistencies for individual hospitals).

At this point in the pandemic, there are few remaining evidences of those policies and procedures in place today, despite the fact that this virus continues to mutate and has made significant gains in transmissibility. As a consequence, nosocomial spread of COVID-19 has been recognized as a growing problem at hospitals in countries where this is measured and reported. We’ll review what we should be learning from those experiences:

1. In the first study we will look at (reference 1), the investigators examined within-hospital (nosocomial) transmission of SARS-CoV-2 among patients and healthcare workers in the UK over two waves – wave 1 (3/1/20 – 7/25/20) and wave 2 (11/30/20 – 1/24/21). At least 32,307 patients are thought to have been infected while in hospitals in England and Wales, and tragically, 414 healthcare workers died between March and December of 2020.

One problem in distinguishing within-hospital (nosocomial) cases from community-acquired cases is the wide-ranging incubation period that we discussed in the last blog piece. Therefore, we tend to use more restrictive definitions for nosocomial infections, which likely means that the number of nosocomial cases is underestimated. A further challenge to identifying cases of hospital-acquired infection is that prior studies have suggested that 33 – 40% of infections are asymptomatic (see e.g., The Proportion of SARS-CoV-2 Infections That Are Asymptomatic: A Systematic Review: Annals of Internal Medicine: Vol 174, No 5 (acpjournals.org)). This, too, likely means that cases of nosocomial COVID-19 are underestimated. One might be tempted to think, “well, if they are asymptomatic cases, then what difference does it make?” There are two reasons that asymptomatic cases still matter. First is that asymptomatic persons still contribute to the transmission of COVID-19. Second, as you will see later in this blog series, asymptomatic cases still pose risk to the infected for long-term health sequelae.

To help get around some of these study limitations, the investigators integrated genomic sequencing to help link cases based on the genetic similarities between samples and location data to identify contacts to augment the main methodology of epidemiological investigation. Using these tools, transmission events could be identified by whether two cases linked by symptom onset were consistent with the serial interval, were in the same hospital location at the time of the suspected transmission event, and if their viral genomes showed a high degree of relatedness.

The investigators determined that during wave 1, of the 1302 cases of COVID-19 detected in the hospitals under the study, 388 cases were determined to be hospital-acquired (nosocomial) infections that, in turn, led to another 85 cases (not included in the 1302) due to subsequent transmission for a total of 473 hospital-acquired infections.

During wave 2, of the 879 cases identified, 350 were identified as hospital-acquired with an additional 52 cases (not included in the 879) due to subsequent transmission for a total of 402 hospital-acquired infections.

Between waves 1 and 2,

• The percentage of all hospital-acquired infections attributed to staff-to-staff transmission declined from 31.6% to 12.9%, while
• The percentage of all hospital-acquired infections attributed to patient-to-patient transmission increased from 27.1% to 52.1%. (These two numbers will not add up to 100% because there can be staff-to-patient and patient-to-staff infections that are not accounted for in these numbers).
• Anywhere between 40 and 50% of hospital-acquired cases resulted in further transmission in the hospital, compared to only 4% of community-acquired cases transmitting onward.

Keep in mind that this degree of in-hospital transmission of COVID-19 was occurring during the time when hospitals were using the most aggressive infection control and surveillance measures of the pandemic, but before the development of substantially more transmissible variants that have been circulating since Omicron at the beginning of 2022 (when many hospitals began letting their guards down).

• There was also a review article (reference 2) of nosocomial COVID-19 published in 2021. The authors make a statement at the beginning of their article, which should come at no surprise to medical directors, chief medical officers, chief quality officers, chief nursing offers and infection control officers in hospitals and health systems:

“Nosocomial infection of COVID-19 directly impacts the quality of life of patients, as well as results in extra expenditure to hospitals. It has been shown that COVID-19 is more likely to transmit via close, unprotected contact with infected patients.”

What does come as a surprise, and in fact, continues to perplex me, is why so many hospitals are ignoring this, even to their own detriment (loss of employee productivity, Long COVID and the loss of some workers at a time of shortages, increases in health plan costs and disability insurance, potential for liability claims, reputational damage, higher costs of care, etc.)

The authors went on to say,

”Additionally, current preventative and containment measures tend to overlook asymptomatic individuals and superspreading events.”

This is very true. In fact, I have asked hospitals who were ending mask requirements, ending testing of all admissions, ending isolation and quarantine measures for their workforce, opening up visitation, and ending vaccine requirements to please do several things:

1. Post plainly for all to see what measures the hospitals are taking to protect patients.
2. Be transparent with reporting on this website the extent of hospital-acquired infections.
3. Outline the thresholds based on community indicators of disease transmission and internal indicators of significant nosocomial spread for implementing additional protections for patients and what those measures would be.
4. Address whether the hospital will respect a patient’s request to have staff mask whenever they enter their hospital room or are otherwise in close contact with the patient.
5. Address explicitly whether your hospital policies require disclosure to the patient that they have developed a hospital-acquired case of COVID-19.

So, far, I am not aware that any hospital has adopted this advice.

Again, nosocomial transmission of COVID-19 is not a rare, or even unusual event. One might come to that conclusion by the lack of attention to this topic and the fact that the CDC does not require hospitals to report this data, but the general rule is that you are not going to find things that you don’t look for. This article references a number of outbreaks.

Well, perhaps the complacency regarding nosocomial COVID-19 is that there are few bad outcomes of COVID-19 acquired in a hospital. What does the data show? One study cited in this review looked at 196 nosocomial COVID-19 cases (NC) out of 1,564 patients from 11 hospitals in the UK and Italy. The mortality rate of NC patients was 27% and the median survival time in NC patients was 14 days. It is important to understand how shocking this is. By definition, persons who develop nosocomial COVID-19 were admitted to the hospital for a different reason – perhaps a broken leg or hip, perhaps to give birth to a baby, perhaps to begin treatment for a newly diagnosed cancer. Whatever the reason, one would have to suspect the intent was to address the problem for which they were admitted for and then return home to their families, their lives and their livelihoods. But more than 1 in 4 of these individuals would die, and with a median survival time of only 2 weeks, one can imagine that many didn’t ever leave the hospital. As a physician and a hospital administrator, I have never seen something this alarming. I often provide advice to immunocompromised patients as to how to remain COVID-19 safe. Many of them have been able to avoid infection for four years now. But, the thing that terrifies them and me is that if they need hospital services, and many will, they will be less safe in a hospital than in their homes. This is outrageous to me. I have never allowed a situation where my patients or those that I am responsible for as a hospital administrator to be less safe in my hospital than they would be at home.

If you were as shocked as I was about the mortality rate for nosocomial COVID-19, you might be thinking that the study referenced was a fluke or an outlier, but it isn’t. We’ll look at one more study:

• This study (reference 3) is a retrospective study of 66 hospital-acquired SARS-CoV-2 cases (out of a total of 435 COVID-19 cases in the hospital during this time) between the dates of March 2 and April 12, 2020 at a major London teaching hospital. Thus, 15% of the total COVID-19 cases being treated were caused by infection after the patient had already been admitted to the hospital for different reasons. The case fatality rate (#deaths/#identified infections) for the hospital-acquired cases was 36%. Now, it would be a fair point to call out that this was prior to the development of many treatments for COVID-19. That is true, but the major reason that the mortality is so high for these patients is that generally, if you have to be hospitalized, you tend to be older and you tend to have numerous underlying medical conditions, all of which place patients at risk for severe infection.

I often hear today a degree of fatalism, such as people are going to get infected no matter what they do. However, that is not necessarily true, and further, the investigators disproved this. They state: “Nosocomial infection rates fell following comprehensive infection prevention and control measures.”

The unanswered question is, why are health care leaders today unwilling to implement comprehensive infection prevention and control measures, especially given that the highest risk patients for severe outcomes of COVID-19 are by their very nature the ones likely to be occupying the majority of their hospital beds?

IV. Proposed changes to the end of isolation

I am not going to prejudge the highly anticipated new guidelines for return to work or school after COVID-19, but I am going to express my hopes. First, just as in my blog posts, I have tried to back my information and opinions up with citations to the science and the evidence, I hope that the CDC’s guidance will be supported with a technical briefing that will clearly demonstrate that their guidance is evidence-based. Second, I hope that the CDC will realize that decisions may need to be individualized. For example, there is a big difference between a person who is a roofer returning to work and someone who works around high-risk individuals (e.g., a worker in a skilled nursing facility or a health aid for the elderly). Third, I hope that the CDC doesn’t use the same rationalization that many have that goes along the lines of, “we are at a different point in the pandemic, everyone has some degree of immunity, and people are no longer overwhelming hospitals anymore.” All of that is true to some extent, but this totally downplays that at this point in the pandemic, we also know that even mild infections can lead to long-term health consequences, that the risks for these long-term health consequences are cumulative, and that we are already seeing the impact on workforce productivity, disability and health care costs. We need for the CDC and public health agencies to stop minimizing the long-term health consequences, while only celebrating the decrease in hospitalizations and deaths (which still have been above 2,000/week for the past couple of months).

I have much more to discuss and update you on in this continuing blog series. Part III will be next.

References:

1. Characterising [sic]within-hospital SARS-CoV-2 transmission events using epidemiological and viral genomic data across two pandemic waves. https://www.nature.com/articles/s41467-022-28291-y.
2. Nosocomial infection of SARS-C0V-2: A new challenge for healthcare professionals (Review) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7891837/.
3. Nosocomial transmission of COVID-19: a retrospective study of 66 hospital-acquired cases in a London teaching hospital. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7337682/.