Two studies published today in JAMA Network Open reveal a 1% COVID-19 infection rate in healthcare workers (HCWs) in hospitals in the southern Netherlands and Wuhan, China, but with higher rates in HCWs who reported no exposure to COVID-19 patients.
The first study, involving 9,705 HCWs screened at two teaching hospitals in Breda and Tilburg, the Netherlands, identified 1,353 who reported fever or respiratory symptoms. Of those workers, 86 (6.4%) tested positive for the novel coronavirus, representing 0.9% of all HCWs. Only 3 (3.5%) reported exposure to a patient who tested positive for COVID-19.
The second study, involving 9,684 HCWs at Tongij Hospital in Wuhan, found that 110 (1.1%) tested positive for the virus. Of 3,110 HCWs dispatched to high-contagion fever clinics and wards to care for 10,830 patients with confirmed or suspected coronavirus, 17 (0.5%) were infected. But of the 4,433 HCWs caring for only non-coronavirus patients, 73 (1.6%) tested positive, as did 20 of 2,012 workers with no patient contact (1.0%).
Expanding case definition to detect more cases
In the Dutch study, which took place in March, researchers found that only 3 of 86 (3.5%) of the infected HCWs had traveled to China or northern Italy, part of the internationally recognized case definition for suspected COVID-19 at the time. But the authors noted that even if they had used a case definition that did not include travel to areas with epidemics, 44 infected HCWs (51.2%) would still have gone undetected.
Most HCWs had a mild illness, 46 (53.5%) had a fever, and 80 (93.0%) met a case definition of fever, cough, and/or shortness of breath. Median age was 49 years (range, 22 to 66), and 71 (82.6%) were women.
When the researchers expanded the case definition to include severe muscle pain (myalgia) and/or general malaise, they were able to capture all 86 infected HCWs. Other common symptoms included headache (49 [57.0%]), nasal discharge (46 [53.5%]), sore throat (34 [39.5%]), chest pain (25 [29.1%]), diarrhea (16 [18.6%]), and loss of appetite (15 [17.4%]).
The first patient confirmed as having COVID-19 in the Netherlands had traveled to northern Italy from Feb 18 to 21. From Feb 27 to Mar 6, of the 127 Dutch COVID-19 case-patients, 9 were HCWs in the two teaching hospitals studied. Eight of the nine reported no recent travel to northern Italy or China, suggesting that SARS-CoV-2, the virus that causes COVID-19, was circulating undetected in the community.
Seven of 86 HCWs (8.1%) said that they began having symptoms before Feb 27. Fifty-four (62.8%) said they had worked while symptomatic. Four (4.7%) had already recovered by the time they were screened, and 19 (22.1%) had recovered by the day they were interviewed, with a median length of illness of 8 days (range, 1 to 20). Two (2.3%) were hospitalized did not become critically ill.
Seasonal flu was also peaking at that time, leading to concerns that infected HCWs would need to take sick leave, diminishing the available healthcare workforce, and raising the risk of introduction of SARS-CoV-2 to the hospitals. This, in addition to observations that HCWs could have COVID-19 and not suspect it, the hospitals implemented voluntary screening from Mar 7 to 12 to determine the prevalence and clinical presentation of infection. By Mar 7, one hospital had nine COVID-19 patients, and the other had five.
The authors said that the HCWs, who were infected within 2 weeks of reports of the first reported Dutch case, likely acquired the virus in the community. "Although we cannot exclude acquisition from known or unknown SARS-CoV-2 infected patients or HCWs to have occurred in some instances, hospital acquisition is unlikely to explain the vast majority of cases coming from more than 50 different departments in two hospitals," they wrote.
Because so many HCWs had only mild illness, nearly half with no fever, the authors recommended expanding the current case definition. "We, therefore, suggest adjusting the currently used case definition for suspected COVID-19 in HCWs by taking fever as one of the possible symptoms and not as a required symptom," they said. "Further improvement of the sensitivity of COVID-19 detection in HCWs can be achieved by adding severe myalgia and general malaise to the case definition."
Non–front-line HCWs at higher risk of infection
In the Chinese study, researchers used a structured questionnaire, electronic medical records, random screening of 335 HCWs, and sampling of hospital surfaces to identify a COVID-19 1.1% infection rate in HCWs in a single hospital. Median age of the 110 infected HCWs was 36.5 years, and 70 (71.8%) were women.
Nurses younger than 45 years who weren't first-line caregivers were more likely to be infected than first-line doctors who were 45 years or older (incident rate ratio, 16.1; 95% confidence interval [CI], 7.1 to 36.3; P < .001).
One of 135 asymptomatic first-line HCWs (0.7%) and 2 of 200 non–first-line workers (1.0%) had subclinical infections. Ninety-three of 110 infected HCWs (84.5%) had mild to moderate illness, and one (0.9%) died. The most common symptoms were fever (67 [60.9%]), muscle pain or fatigue (66 [60.0%]), cough (62 [56.4%]), sore throat (55 [50.0%]), and muscle ache (50 [45.5%]).
The main routes of COVID-19 exposure were believed to be contact with infected patients (65 [59.1%]) or infected coworkers (12 [10.9%]), and community transmission (14 [12.7%]). Nineteen HCWs (17.3%) did not recall their exposure history. None had been to the Huanan seafood market believed to be the outbreak epicenter, but 13 (11.8%) had been to other live-animal markets.
More first-line HCWs were infected in fever clinics or wards than non–first-line HCWs (7 [41.2%] vs 0), and fewer first-line HCWs were infected in general wards or clinics (6 [35.3%] vs 64 [68.8%]) (P < .001).
In low-contagion areas of the hospital, HCWs wore surgical masks, latex gloves and gowns, and disposable round caps. In high-contagion areas, they wore fit-tested particulate respirators equivalent to N95 respirators, long-sleeved gowns, goggles, disposable round caps, latex gloves, and shoe covers. No environmental surfaces tested positive for live coronavirus.
Noting that most infections occurred in HCWs working in low-risk areas, the authors recommended routine screening of all staff, including those who are asymptomatic.
"In this study, non–first-line HCWs were at a high risk of infection during the early stage of the COVID-19 outbreak," before protective measures were implemented, "and interventions targeting this group should be evaluated," they wrote.
Infection control measures effective
In a commentary in the same journal, Vincent Chi-Chung Cheng, MD, and Shuk-Ching Wong, MNurs, of Queen Mary Hospital in Hong Kong, and Kwok-Yung Yuen, MD, of the University of Hong Kong, said that patients with subclinical or asymptomatic infection may have spread the coronavirus in low-risk areas, particularly during aerosol-generating procedures, in the Chinese hospital.
They said that hospitals should pay special attention to careful collection and handling of respiratory samples, infection-control measures, and wearing personal protective equipment, because they have been shown to work.
"It is reassuring that the frontline HCWs in China and the Netherlands had low rates of nosocomial [hospital] acquisition of COVID-19," they wrote. "This suggests that infection control measures are effective and should be escalated in response to the rapidly evolving epidemic to provide maximal protection to our HCWs and patients."