Four papers on CoV-2 transmission
17 April 2020. Related: COVID-19: transmission & prevention, COVID-19.
These following four papers are interesting for different aspects relating to CoV-2 transmission
A paper in the New England Journal of Medicine from Zou et al reported similar levels of viral load in an asymptomatic patients and symptomatic patients which suggests the transmission potential of people who are asymptomatic or minimally symptomatic.
Two other papers are examples of CoV-2 failed to be transmitted even to people at high risk and might help reduce anxiety for contacts of people who are later diagnosed with COVID-19.
The first describes the first person-to-person transmission in the US between partners at home. However, 347 contacts of other cases including 152 community contacts and 195 health workers found no other transmissions. This included 43 people under special investigation who all tested negative for SARS-CoV-2. 
The second, also from the US, included a case of someone diagnosed with COVID-19 but with mild symptoms who continued to remain PCR positive for 18 days after diagnosis. However, there were no further transmissions to 16 contacts. Of these 11/16 (69%) had high-risk exposure, including 1 intimate contact, and 5 (31%) had medium-risk exposure. 
Lastly, a retrospective study, but before peer-review, of household transmission in Wuhan, after the city had been locked down, reported that each index case resulted in approximately three other infections. 
Of the 85 original cases, there were 155 close contacts overall. Of these, 104 contacts received PCR testing, with 47 (30%) positive cases and 57 (37%) negative cases. The other 51 (33%) cases were not tested because they were asymptomatic during the 2 weeks of quarantine. The infection rates were 38%, 50% and 31% for households with one, two and three contacts, respectively.
- Zou et al SARS-CoV-2 viral load in upper respiratory specimens of infected patients. N Engl J Med 2020 382:1177-1179. DOI: 10.1056/NEJMc20017372020. (19 March 2020).
- Ghinai I et al. First known person-to-person transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the USA. The Lancet. DOI:10.1016/S0140-6736(20)30607-3. (13 March 2020).
- Scott SE et al. First mildly ill, non-hospitalized case of coronavirus disease 2019 (COVID-19) without viral transmission in the United States — Maricopa County, Arizona, 2020, Clinical Infectious Diseases, ciaa374, DOI: 10.1093/cid/ciaa374. (02 April 2020).
4. Wang Z et al. Household transmission of SARS-CoV-2. J Infect. 2020, doi: 10.1016/j.jinf.2020.03.040.