COVID-19 has become endemic to the Chinese city of Shenzhen, and a sharp increase in pediatric infections may indicate that community and intra-family transmissions have become the new mode of spreading the virus, according to a study published yesterday in Emerging Infectious Diseases.

Also, in a research letter published yesterday in the Journal of Infection, researchers described and compared the wide range and changing characteristics of COVID-19 infection on computed tomographic (CT) imaging with clinical manifestations to improve diagnosis.

Shifting characteristics in Shenzhen

Led by researchers at the Third People's Hospital in Shenzhen, the study analyzed clinical and epidemiologic characteristics of the city’s first 365 COVID-19 patients with laboratory-confirmed disease, including 74 clusters of 183 cases. The median patient age was 46 years (range, 1 to 86 years), and the cases were split evenly between males and females.

To investigate the shift of the epidemic, the researchers compared patient characteristics before Jan 24 with those from Jan 25 to Feb 5. "Compared with before Jan 24, the proportion of case-patients without definite exposure was much higher from Jan 25 through Feb 5 (11% vs. 6%; P < 0.001) and increased to 36% (12/33) on both Jan 31 and Feb 5," the authors wrote.

They also reported a sharp increase in the proportion of infected children (2% before Jan 24 to 13% for Jan 25 to Feb 5; P < 0.001), meaning that increased exposure for children and familial transmission could contribute substantially to the epidemic.

The researchers noted that the steep increase could be attributed to the low proportion of children exposed early in the outbreak; early detection for children who had had close contact with people with diagnosed or suspected infection after control measures were implemented; or failure to identify the relatively mild signs and symptoms in children, especially because resources were limited early in the Wuhan outbreak.

The investigators caution that delays from infection to illness onset or onset to confirmation may have biased the comparisons.

After Jan 17, infections increased substantially and peaked Jan 22 to 30. The authors said that the decline since then is probably due to both under-identification of cases of recent onset and delayed identification or reporting.

Interval from exposure to symptom onset

Of 56 clusters of single co-exposure cases, the mean interval of symptom onset between the primary and second case-patient in a cluster was 3.1 days. The mean interval of symptom onset between the primary and last case-patient within a cluster was 3.6 days.

After strict control measures were implemented, the researchers observed a shortened span from illness onset to hospital visits (median days declined from 3 to 1; P < 0.001).

Recommendations to contain spread

The investigators recommend that infected patients be treated at designated hospitals to decrease the risk of nosocomial transmission. However, they found that only 13% to15% of infected patients went to the city's designated hospital first. "This finding means that a substantial number of case-patients visited > 1 nondesignated hospital before they were admitted to the designated hospital, which increases the risk for nosocomial infection," they wrote.

"Early screening, diagnosis, isolation, and treatment are necessary to prevent further spread," the researchers wrote. "Strengthening effective and efficient measures, including but not limited to personal protection within families and communities with a high risk for exposure, will prevent and interrupt community and intrafamily transmission."

Shenzhen is a city of 13 million people in southern China.

Varied CT, clinical findings

In the second study, researchers at Sun Yat-sen University in Guangzhou, China, detailed the CT findings and clinical characteristics of six women 27 to 63 years old with COVID-19.

None of the patients had such underlying diseases as diabetes, cancer, or respiratory disease. Five had had Wuhan or Hubei exposures.

They found that COVID-19's wide variety of manifestations on CT can vary over time. Early in the disease, lesions can appear round and nodular in the central lung, unlike their common patchy appearance between the membrane surrounding the lung and the body wall. One patient had 3 follow-up scans 4 to 14 days later that showed diverse lesions and that the primary lesions had been absorbed and replaced elsewhere by new ones.

On testing blood samples, the researchers observed normal or slightly decreased counts of leucocytes and lymphocytes and identified mildly decreased eosinophil counts in four of the patients. Four days later, follow-up testing revealed that the low eosinophil counts remained abnormal and had dropped even further. "The decrease of eosinophil count may be helpful for the early diagnosis of the disease," they wrote, calling for further study of the phenomenon.

They also commented on the high false-negative rate in the oropharyngeal swabs used to diagnose and confirm COVID-19 infection and called for an alternative technique to be developed as soon as possible.

Serious symptoms unlikely in pregnancy, study finds

In other research news, pregnant women are not at increased risk of having severe symptoms of COVID-19 infection, according to an analysis of 147 women in Wuhan published Friday by the World Health Organization and China.

The analysis found that only 8% of the women had serious illness, and 1% were critically ill.

This is in contrast to other respiratory infections that easily infect pregnant women and can cause serious illness, with long-lasting consequences for them and their babies. While long-term effects on the babies are unknown, a small study published in February in The Lancet showed that the newborns of women infected with COVID-19 appeared healthy and virus-free after cesarean delivery and isolation from their mothers.