The coronavirus disease (COVID-19) is rapidly spreading across the globe, and containment measures have been implemented at many of the hotspots for the disease. Though isolation and quarantine measures are considered the best way to contain the virus, one new study suggests it might not be as effective as hoped.
The study, published in the International Journal of Infectious Diseases, by researchers from Japan, shows that the virus's serial interval, which is the period between successive cases, is close to or shorter than its median incubation period. This means that people can transmit the virus even if they have no symptoms, causing the vast spread of the virus.
The coronavirus disease outbreak has already spread to more than 100 countries, with 3,825 deaths and a staggering 110,041 confirmed cases, mostly in mainland China. Italy has surpassed South Korea as the country with the highest number of cases outside China, with 7,375 cases and 366 deaths. South Korea has 7,382 confirmed cases with 50 deaths, while Iran has 6,566 cases and 194 deaths.
Novel Coronavirus SARS-CoV-2 This scanning electron microscope image shows SARS-CoV-2 (yellow)—also known as 2019-nCoV, the virus that causes COVID-19—isolated from a patient in the U.S., emerging from the surface of cells (pink) cultured in the lab. Credit: NIAID-RM
What is a serial interval period?
The serial interval refers to the time between successive cases in a chain of transmission. It can be estimated as the period between infection and subsequent transmission, or the onset of symptoms with the primary patient and the start of symptoms with the secondary patient, who was infected by the primary patient.
In the case of the coronavirus disease, the serial interval is between 4.0 and 4.6 days. The team of researchers at Hokkaido University in Sapporo conducted the study, which is crucial in determining measures to prevent further spread of the virus. It also enables the identification of epidemiologic links between confirmed cases.
"When the serial interval is shorter than the incubation period, the pre-symptomatic transmission is likely to have taken place and may even occur more frequently than symptomatic transmission," the authors wrote in the study.
"A short serial interval makes it difficult to trace contacts due to the rapid turnover of case generations," they added.
The study findings
To arrive at the results, the researchers estimated the serial interval of COVID-19 by using data from 28 pairs of infector-infectees. The team collected dates of illness for primary cases, called infectors, and secondary cases or infectees from published articles and case reports.
To gather data, they subjectively ranked the legitimacy of the data. They studied both the full dataset of 28 patients and a subset of pairs that had the highest certainty in reporting. They gauged the median serial number to 4 days at first, and after adjustments to most certain pairs, they had 4.6 days. Hence, the team estimated the serial interval is between 4 to 4.6 days.
Health officials call for global preparedness amid the coronavirus outbreak, urging countries to lay down plans to contain the virus. Hong Kong, for one, is an excellent example of virus containment, especially among healthcare workers.
Hong Kong hospital protected its healthcare workers
Another new study highlighted how a hospital in Hong Kong had achieved a zero infection status among its healthcare workers. In this study published in Infection Control & Hospital Epidemiology, the researches discussed and described the hospital's infection control response in the first 42 days after the outbreak in Wuhan City, China started.
The outbreak emerged in a seafood market in Wuhan City, in the province of Hubei Province, where most of the cases and deaths occurred. In late December 2019, a cluster of cases showing pneumonia-like illness has been reported, raising an alarm of a potential novel virus. The virus has quickly spread to other provinces and other regions, including Hong Kong.
The hospital promptly ramped up its infection control measures by using enhanced laboratory surveillance, early airborne infection isolation, fast diagnostic testing, and contact tracing for healthcare workers, who were unprotected during the exposure.
Apart from these measures, the hospital also made sure to educate their workers about personal protective equipment, infection control, and proper hand hygiene. Further, when a patient tested positive for coronavirus, he or she was immediately placed on isolation in an airborne isolation ward with at least one-meter space between patients.
Effective infection control measures
All the precautionary measures implemented in the hospital have led to zero infections or deaths among hospital workers. The eleven healthcare workers who were unprotected when they were exposed were placed on quarantine for 14 days. There had been no infections among hospital workers, and there are no hospital-acquired infections in the first six weeks of the outbreak.
The hospital at that time was catering for 1,275 patients with suspected infection and treating 42 confirmed cases.
"Appropriate hospital infection control measures could prevent nosocomial transmission of SARS-CoV-2 (severe acute respiratory syndrome coronavirus type 2)," the researchers wrote in the paper.
How did the hospital do it? The authors said that the hospital had imposed strict measures such as vigilance in hand hygiene practice, wearing of surgical masks in the hospital, the appropriate use of PPEs in patient care and in performing aerosol-generating procedures, all contributed to preventing hospital-acquired infection and the spread of the novel coronavirus.
The team also found that environmental transmission is not as crucial as human-to-human transmission, suggesting that close contact with an infected patient will more likely transmit the virus. The team collected air samples from near the mouth of a patient with the virus and tested the objects in the room. They found no virus in the samples, except on a window bench.
Public containment success in Hangzhou
An accepted manuscript for the journal Infection Control & Hospital Epidemiology as part of the Cambridge Coronavirus Collection focussed on Hangzhou, the capital of Zhejiang province in China. China has been the hotspot of the coronavirus outbreak. Though Hubei province reported tens of thousands of cases, Hangzhou in China had an efficient means of virus containment. The swift public health response in the province caused the infection toll to decrease. Between January 19 to 27, there were 169 cases, while there was just one case diagnosed between Feb. 17 and 20. The province reported no deaths.
In the province, only one family member was permitted to leave the family home and buy essentials every two days. Further, health officials imposed a package delivery method involving no close contact with clients. Employees and students also stayed at home, working and studying online, while chartered transportation helped migrants return to their workplaces.
The province also has a system with green, yellow, and red codes. Residents were classified into these three codes - a green code means that there is a low risk of infection, a yellow code, and red code mean they need to be subjected to quarantine for 7 to 14 days while reporting their health status daily until they reach the green code.
The measures were useful in the province, and it can be effective in other countries affected by the outbreak.
- Nishiura, H., Linton, N., and Akhmetzhanov, A. (2020). Serial interval of novel coronavirus (COVID-19) infections. International Journal of Infectious Diseases. https://www.ijidonline.com/article/S1201-9712(20)30119-3/fulltext
- Cheng, V., Wong, S.C., Chen, J., Yip, C.et al. (2020). Escalating infection control response to the rapidly evolving epidemiology of the Coronavirus disease 2019 (COVID-19) due to SARS-CoV-2 in Hong Kong. Infection Control & Hospital Epidemiology. https://www.cambridge.org/core/journals/infection-control-and-hospital-epidemiology/article/escalating-infection-control-response-to-the-rapidly-evolving-epidemiology-of-the-coronavirus-disease-2019-covid19-due-to-sarscov2-in-hong-kong/52513ACC56587859F9C601DC747EB6EC
- Diao, M.Y., Zhang, S., Chen, D., and Hu, Wei. (2020). The novel coronavirus (COVID-19) infection in Hangzhou: An experience to share. Infection Control & Hospital Epidemiology. https://www.cambridge.org/core/journals/infection-control-and-hospital-epidemiology/article/novel-coronavirus-covid19-infection-in-hangzhou-an-experience-to-share/17FC89BD070E528F33044D9488414BF3