I am seeing masks with just one layer even though it was said many times that a proper mask should be with three layers. Why are these still being sold? – Tiziana Attard Pizzuto

The World Health Organisation has issued evidence-based guidelines, which specify that homemade fabric masks should have three layers to be most effective. 

The layers should include an inner layer that is absorbent, such as cotton, a middle layer that acts as a filter made of non-woven material such as polypropylene, and an outer layer made from a non-absorbent material like polyester or polyester blend.

Fabric masks should be cleaned regularly and worn correctly. Other precautions need to be taken as masks alone will not protect completely from COVID-19.

Masks are not a replacement for physical distancing, hand hygiene, and other public health measures.

What is the R factor at present? – Sharon Maria

At present the R factor is above 1.

The reproduction number (R) is the average number of secondary infections produced by a single infected person. An R number of one means that on average each person who is infected will infect one other person, so the situation is stable.

If R is greater than one the spread is growing and if R is less than one the spread is decreasing. The R factor, hence, shows the direction of change.

There are various factors which affect R factor and should not be used as a single parameter to monitor how the pandemic in changing. ECDC is using growth rate to provide information on the size and speed of change. An important indicator is the number of new cases of the disease identified during a specified time period (incidence). The R factor has varied along the weeks of the pandemic with variations above and below 1.

What percentage of positive tests give false positives? And vice versa, how many were false negatives? – Simon Oosterman

The likelihood of obtaining a false-positive or false-negative diagnostic test result is influenced by factors related to the testing scenario and the test being used.

Diagnostic tests perform optimally for detecting an infection when the pre-test probability is high. Pre-test probability is the likelihood that the person being tested actually has the infection.

This likelihood is based on both the proportion of people in the test population or group who have the infection at a given time (prevalence) and the clinical presentation (including symptoms and known exposure) of the person being tested.

In other words, the pre-test probability increases with increasing prevalence in the population and clinical indications of illness in the person being tested. In contrast, tests typically perform best for excluding an infection when the pre-test probability is low.

Test sensitivity is the ability of a test to correctly identify persons with infection, whereas test specificity is the ability to correctly rule out infection.

My daughter, a seven-year-old girl, is looking forward to starting school but afraid at the same time because of the swab test. Is it possible to introduce a different method of swab testing our children? – Ritianne Fenech

Symptomatic children should stay at home. It is important to contact the doctor to see if testing is needed. Testing might be recommended for a child who currently has symptoms of COVID-19 or who was in close contact with someone with COVID-19. For contacts of cases, these will be guided by the public health contact tracing team.

A diagnostic test for COVID-19 can show if your child has the infection at the time of the test. The molecular test analysed at the laboratory by means of PCR (polymerase chain reaction) is the gold standard test for diagnosis. It uses a nasopharyngeal swab. Further tests are being evaluated.

Are children or adolescents less susceptible to COVID-19? – Joan Borg

Research indicates that children and adolescents are just as likely to become infected with COVID-19 as any other age group and can spread the disease to others during the infectious period.

What is seen from the limited evidence is that children and young adults are less likely to get severe disease, but severe cases can still happen in these age groups especially in those children who have underlying medical conditions which put them at increased risk of complications.

Anyone, including children, should follow the same guidance on self-quarantine and self-isolation if there is a risk they have been exposed or are showing symptoms. It is particularly important that children avoid contact with older people and others who are at risk of more severe disease.

Charmaine Gauci, Superintendent for Public Health.

Have a health-related question you'd like answered? E-mail: askcharmaine@timesofmalta.com