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Paradigm Shift Intervention Monitoring
Coronavirus Transmission By Mild Case
On 5 February, an adult member of the same extended family of the two confirmed cases – who had not travelled abroad – developed an influenza-like illness. The illness remained mild, not requiring hospital admission, and there has been a full recovery. A sputum sample from this case was later confirmed to contain novel coronavirus. This case had limited exposure to the index case on three occasions while the latter was in hospital, and had no contact with the second case.
The routes of transmission to humans of the novel coronavirus have not yet been fully determined, but the recent UK experience provides strong evidence of human-to-human transmission in at least some circumstances. The limited contact that one of the cases had with the index case, however, leaves open the possibility of an intermediary case within the extended family.
The above comments are from a February 19 HPA report (which is no longer linked at HPA site) on the four confirmed nCoV cases in the UK. The description of the two cases who developed symptoms in the UK, raises concerns that the mild case (30F, sister of the index case) was infected by a symptomatic family member, since the confirmed case had no contact with the fatal case (38M, son of index case).
The recent Eurosurveillance paper which detailed the cluster noted that PCR testing of contacts, including asymptomatic contacts, failed to identify additional cases. Consequently, none of the other family members were classified as probable cases, based on the WHO definition of a probable case (symptomatic contact who could not be tested). However, that paper noted that both of the family members described above also tested positive for type 2 human parainfluenza virus (HPIV-2), which raises the strong possibility that both were infected by another family member, since no evidence has been presented that the index case (60M) was infected with HPIV-2. Moreover, the sister had limited contact with the index case (three hospital visits while the patient was under mechanical ventilation). In addition, the disease onset dates for the two family members differed by one day, supporting a common source for these two cases.
Infection by a third family member who tested negative for nCoV and had mild symptoms (no hospitalization) would have serious implications (like SARS-CoV, detection of nCoV in mild cases is a challenge).
In addition to the two confirmed cases positive for HPIV-2, two contacts also tested positive for HPIV-2. Detail on these two cases, as well as sequencing of HPIV-2 from all four cases, would be useful.