Study: COVID-19 Symptoms Take Days to Manifest

(CN) – Individuals infected with the coronavirus COVID-19 may go between 5 and 12 days before displaying any symptoms, according to research released Monday.

The findings, published in the journal Annals of Internal Medicine, support current recommendations by the U.S. Centers for Disease Control and Prevention for health care providers to actively monitor patients for 14 days after an assumed exposure to COVID-19 and contain important implications for informing control activities.

A U.S. Centers for Disease Control and Prevention illustration of COVID-19, a novel coronavirus.

In December of 2019, a cluster of severe pneumonia cases of unknown etiology was reported in Wuhan, Hubei province, China. Soon after, the cases were attributed to a novel strain of coronavirus closely related to the same family of viruses that Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), and the four human coronaviruses associated with the common cold.

The term coronavirus refers to a large family of viruses and the latest has been coined COVID-19 – CO- for corona, VI- for virus, D- for disease, and 19 for the year of its discovery. Some coronaviruses only affect animals, including camels, cattle, cats, and bats, and though it is rare for these animal-specific viruses to infect humans it is suspected to have happened in Wuhan.

At the beginning of the spread, many of the patients had some connection to a large seafood and live animal market. Many later patients did not share this link, raising questions about how the disease spreads. It is thought to travel person-to-person between individuals within six feet of each other, most likely through sneezing and coughing. It is also possible for the virus to spread via an individual touching surfaces that contain traces of the virus, and then touching their mouth, nose, or eyes, though the CDC explains that this would not be the main way the virus spreads.

Infected patients can be asymptomatic or experience mild to severe symptoms including a high fever, a persistent cough and shortness of breath. COVID-19 is a respiratory disease, so the elderly and individuals with severe underlying health conditions, including heart disease, lung disease and diabetes are at an increased risk.  Additionally, our current understanding of the incubation period for COVID-19 is limited.

As of Monday, there have been 423 confirmed cases across 35 states and the District of Columbia and so far 19 deaths. The CDC says 72 cases are travel related, 29 are from person-to-person spread and 322 are under investigation, though the agency notes the most accurate data will come from the health departments of affected states.

For Monday’s study, researchers from Johns Hopkins Bloomberg School of Public Health conducted a cumulative analysis of COVID-19 data from news reports, public health reports, and press releases from 50 provinces, regions, and countries outside of Wuhan, China. With this data, they were able to estimate the length of the incubation period of this virus – the time from exposure to the onset of symptoms.

Using vital information on roughly 181 confirmed cases with identifiable exposure and symptom onset windows, the researchers estimated that the median incubation period of COVID-19 at about 5.1 days. About 97.5% of those who develop symptoms appeared to do so within approximately 11.5 days of infection. These estimates imply that on average, 101 out of every 10,000 cases will develop symptoms after 14 days of active monitoring or quarantine, which further supports the current CDC recommendations.

The study authors emphasize caution that given the recent evidence of the virus being transmitted by mildly symptomatic and asymptomatic individuals, the time from exposure to onset of infectiousness – known as the latent period – may actually be shorter than the estimated incubation period, with important implications for transmission dynamics.

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