In November 2020, almost 5% of older people from Lombardy region reported having had signs or symptoms compatible with COVID-19 or having been tested positive for SARS-CoV-2 infection based on a nasopharyngeal swab or a serological test. No relationship between sex or level of education and SARS-CoV-2 infection was observed. Subjects aged 65-69 years more frequently reported to have been infected compared to older subjects. Having one or more chronic diseases were related to a lower rate of infection. SARS-CoV-2 infection resulted being a determinant of a worsening in depressive symptoms.
Based on our data, after almost one year from the beginning of the COVID-19 pandemic, 2.2% of adults aged 65 and older from the Lombardy region reported having had a positive nasopharyngeal swab. In November 2020, corresponding official data from the Italian National Health Institute showed that the cumulative incidence was around 3.5% in Italian adults aged 60 or more and around 3.8% in the Lombardy general population9. The lower prevalence of people who tested positive on a swab detected within our survey might be explained by the exclusion from our sample of the individuals residing in nursing homes, and subjects who died within the 2020 due to the infection.
However, it is interesting to note that the percentage of participants who have been infected rose by 50% (reaching 3.3%) when adding those who declared having tested positive for the serological test, and potentially more than doubled (up to 4.9%) when adding those who experienced signs or symptoms compatible with COVID-19 without any test confirmation. These results might be explained by the fact that, in Italy, in the early stages of the pandemic, the performance of nasopharyngeal swabs was almost exclusively addressed to patients in severe conditions, thus excluding a large number of individuals with none or mild signs or symptoms10. Accordingly, the Italian Ministry of Health conducted a seroprevalence study between May 25, 2020, and July 15, 2020, which revealed that 7.5% (95% CI: 6.8 – 8.3) of the Lombardy general population had SARS-CoV-2 antibodies11, confirming the fact that the real cumulative incidence is underestimated when considering only nasopharyngeal swab data.
With regard to the determinants of infection, an important clarification must be made.
Since COVID-19 is characterized by non-specific signs and symptoms12 some of which can be very common in the elderly population13,14, as a sensitivity analysis, we excluded subjects reporting only signs or symptoms without a confirmed diagnosis.
We did not observe any significant relationship between sex and SARS-CoV-2 infection, although our data seem to suggest a marginally higher prevalence of infection in males. This is partly in line with a recent systematic review 15, that found men having a slightly higher frequency of infection16,17.
We found a lower frequency of infection in participants aged 70 years or older than in participants aged 65-69 years. This result could be explained by the fact that the latter group included a higher proportion of working subjects, likely more exposed to SARS-CoV-2 infection because of more frequent social interactions. In addition, since social isolation increases with age18, it is conceivable that subjects aged 70 years or more, having had fewer interactions, were better able to protect themselves from possible opportunities for infection. It is also likely that older people, aware of the higher risks to which they were exposed, were more careful to comply with preventive measures19. Our finding is in line with a large systematic review and meta-analysis including 241 seroprevalence studies showing that the proportion of individuals aged 65 years or older with SARS-CoV-2 antibodies tended to decrease with age16. Also, data from an Italian Ministry of Health survey show a decrease in seroprevalence in the over-70 age group compared to the 60-69 age group11. Since our survey did not allow for the inclusion of those who died of COVID-19, we recalculated the prevalence in every age group considering the number of expected cases, which is obtained by adding the proportion of deaths per age group based on the case fatality rate provided by the National Health Institute referring to November 20209. The cases distribution by age remained substantially unchanged.
Participants residing in the neighboring provinces of Bergamo and Brescia showed a higher infection rate than participants from the Milan province. These results reflect data from seroprevalence studies in Lombardy17,20. In line with other studies21,22, compared to married or cohabiting subjects, divorced and separated ones more frequently reported SARS-CoV-2 infection. However, the reasons for this finding are unclear.
The absence of chronic diseases was associated with a higher frequency of infection. This can be explained by a less cautious attitude of this sub-group compared to individuals with at least one chronic condition who were probably aware of the increased risks they were facing. In fact, the presence of specific chronic diseases leads to a depression of the immune system23 and an increased risk of COVID-19 resulting in adverse outcomes5. This has been shown particularly among patients with diabetes. By contrast, patients reporting having been diagnosed with some forms of chronic migraine before the COVID-19 pandemic showed a higher infection rate.
Both COVID-19 and Post COVID-19 Syndrome can occur with migraine24,25, however our results seems to suggest that this condition could also result in an increased risk of infection. Further studies are needed to clarify this relationship.
A higher frequency of infection was observed in subjects reporting a worsening of depressive symptoms during the pandemic. Evidence from the literature shows that people who suffered from COVID-19 frequently experienced a deterioration of their mental health25–28. Furthermore, people who reported being infected most likely had other cases in their family 29 and may have lost relatives as a result of COVID-19. The likelihood of reporting signs and symptoms referrable to COVID-19 may be related to the presence of depression and/or anxiety: studies comparing the prevalence of anxiety and depression among subjects who tested positive and subjects who tested negative to SARS-CoV-2 infection found different results30,31, so further research is needed to understand the nature of this relationship.
Our findings should be interpreted in light of some limitations. The first one to mention is that data on diagnostic tests and COVID-19-like signs and symptoms were self-reported, this exposes to potential recall bias. Furthermore, it must be considered that testing capacity in Italy changed during 2020 and that some participants may have passed through an asymptomatic SARS-CoV-2 infection without ever being tested. Moreover, as this is a cross-sectional study, we could not establish any causal relationship, although all efforts have been considered to give a longitudinal context to the analyses. However, to the best of our knowledge, this is the first study that investigates the role of possible determinants of SARS-CoV-2 infection in older people. We also believe that this study provides useful elements to obtain a more reliable estimate of the magnitude of the cumulative incidence of COVID-19 in this population than data on nasopharyngeal swabs alone. Furthermore, we used a large representative sample of the population aged 65 or more from the Lombardy Region, and data were collected through a telephone-based interview, which can be considered the most suitable solution for the older population in a pandemic context. In fact, during the pandemic, online surveys proved to be an effective tool for overcoming social distancing measures32, but they carry the risk of selection bias since they exclude those who, like many seniors, have poor digital literacy and internet access33.
In conclusion, our results suggest that the oldest old subjects and those having chronic conditions limited their exposure to SARS-CoV-2 infection. Although the COVID-19 case fatality rate increases dramatically after the age of 7034, our study seems to indicate that those between the ages of 65 and 69 are more susceptible to SARS-CoV-2 infection and should be targeted by preventive strategies to better contain the spread of contagion.