SOURCE: Frediani JK, Parsons R, McLendon KB, et al. The new normal: Delayed peak SARS-CoV-2 viral loads relative to symptom onset and implications for COVID-19 testing programs. Clin Infect Dis 2023; Sep 28:ciad582. doi: 10.1093/cid/ciad582. [Online ahead of print].
Many times over the past year, I have heard friends and patients who have had symptomatic respiratory infection exclaim that serial home COVID antigen (Ag) tests were repeatedly negative for COVID, but then on the third or fourth day of symptoms, tested positive. This is a different experience than that observed during the earlier years of the pandemic, when kits were first available, and we depended on people to provide home testing results on the first or second day of illness. This apparent change in the performance of the rapid Ag test has not been well characterized — nor really communicated to the public.
In an effort to characterize the hypothetical utility of rapid Ag kits, these authors examined cycle threshold (CT) values in symptomatic adults infected with SARS-CoV-2 relative to the onset of symptoms. From April 2022 to April 2023 (during Omicron), adults presenting with respiratory symptoms had nasal swabs obtained for multiplex Xpert Xpress testing (Cepheid GeneXpert Xpress SARS-CoV-2/Flu/RSV RT-PCR assay). Information on the type and duration of symptoms and history of COVID vaccination was collected, along with information on prior testing within the previous two weeks. SARS-CoV-2 CT values ≤ 30 or ≤ 25 were used as cut-offs for assessing the potential hypothetical performance of rapid Ag testing. No information on influenza vaccination was available.
A new SARS-CoV-2 infection was diagnosed in 348 individuals: 65% were women, the median age was 39 years, and 91% gave a history of vaccination, prior infection, or both. Symptoms included cough (81%), sore throat (79%), and rhinorrhea/congestion (75%). CT values rose from the first day of symptom onset and peaked at day 4-5 of illness. Based on CT values ≥ 30, the estimated sensitivity of rapid Ag testing would be about 30% to 60% on the first day of symptoms, 59% to 75% on the third day of symptoms, and 80% to 93% on the fourth day of symptoms.
For comparison, there were 273 symptomatic adults who reported a positive COVID test within the previous 14 days (by any method). Prior vaccination and/or infection was reported in 87.5% of this group. CT values peaked at the third to fourth day of symptoms.
A smaller group of 74 individuals were PCR+ for influenza. CT values for two influenza targets peaked shortly after symptom onset on day 1 and generally decreased on day 2-3, although some patients remained positive for five to seven days.
Home Ag kits may perform differently than previously expected, with reduced sensitivity at days 1-3 of symptom onset and peak utility at days 4-5 of symptoms. Whether this delayed peak in detection is due to changes in immunity from prior vaccination and/or infection or differences in SARS-CoV-2 strains is not understood. This finding has significant implications for home use of these kits, as well as the use of these kits in the institutional setting when attempting to “clear” individuals. Multiplex kits being developed for use in the home would provide very different sensitivities for influenza and COVID depending on the day of testing relative to symptom onset. This may be difficult to explain to the public, but at the least would require serial testing to improve test reliability.
SOURCE: Diekama DJ, Nori P, Stevens MP, et al. Are contact precautions “essential” for the prevention of healthcare-associated methicillin-resistant Staphylococcus aureus? Clin infect Dis 2023; Sep 21:ciad571. doi: 10.1093/cid/ciad571. [Online ahead of print].
The Society for Healthcare Epidemiology of America and the Infectious Diseases Society of America, as well as the Centers for Disease Control and Prevention (CDC), all continue to recommend infection control contact precautions (CP) for patients with methicillin-resistant Staphylococcus aureus (MRSA) infection or colonization. However, even in our immediate area, while several acute care hospitals continue to isolate and apply CP for such patients, others have chosen to apply CP only for those patients with MRSA infection and not colonization, and a few have abandoned this practice altogether.
In California, it is a regulatory requirement to provide nares MRSA screening for high-risk individuals, which can be variously defined but at the least includes all admissions to the intensive care unit (ICU). Our facility also provides nares screening for all patients admitted from skilled nursing facilities (SNFs) or long-term care, and those on hemodialysis. About 11% are colonized on admission. Once recognized, they are isolated, infection control flags their chart, and CP are implemented. Our facility even has extended this practice to pre-emptively place patients admitted from several high-risk SNFs known to be “endemic” for MRSA/multidrug-resistant organisms (MDRO)/carbapenem-resistant Enterobacterales (CRE) in isolation until the results of admitting screening studies have been completed.
These authors questioned the merits of isolation and CP for patients with MRSA. They identified studies that support this practice, usually combined with other measures, but also identified studies that could not definitively demonstrate a benefit for the use of gown and gloves in the prevention of MRSA transmission. Part of the problem is that many studies employ a bundle of infection prevention practices for patients with recognized MRSA colonization, including enhanced hand hygiene and environmental cleaning, regular chlorhexidine bathing, and sheet changes, and, thus, teasing out the specific benefit of gowns/gloves is not possible.
An argument against the need for isolation and CP for hospitalized patients with recognized MRSA colonization or infection is the fact that even with routine nares screening, many such patients escape detection, and yet MRSA transmission or outbreaks in facilities are not commonly observed. Nares MRSA screening (by any method) identifies only about two-thirds of patients with colonization. Because of the expediency and more limited resources during COVID, our facility abandoned isolation and CP practices for MRSA for two years and did not observe an increase in MRSA transmission. Of course, many patients were in isolation for COVID.
In contrast to any purported benefit of CP, the authors argue there is clear evidence of harm from such practices, including reduced staff-patient interactions, with detrimental effects on patient experience and well-being. Some facilities have more limited resources, and this practice may not be as valuable as other interventions, as well as the general waste of unnecessary gowns and gloves, and the added impact to the environment.
Instead of the routine isolation of MRSA-positive patients, the authors argue that isolation and CP should be employed only when increased transmission is observed.
We have debated these issues ourselves, recognizing that we do not observe much evidence of MRSA transmission in our facility. Most cases of hospital-onset MRSA infection are presumed to have had unrecognized colonization, and in-hospital transmission has not been a significant problem. On the other hand, staff “fatigue” with infection control practices is a real problem. Perhaps it is best to focus preventive efforts on more worrisome organisms with a greater potential for risk, such as CRE and Candida auris. But for now, as long as CP continue to be recommended by the CDC, many facilities will continue this practice.
