Most Important Infectious Diseases Among Those Greater Than or Equal to 65 Years
Most Important Infectious Diseases Among Those Greater Than or Equal to 65 Years
This study on notification rates of ID and trends over 19 years among the general Norwegian population ≥65 years shows that invasive bacterial diseases, and specifically invasive pneumococcal disease, were most common and occurred more often among older compared to younger individuals. Furthermore, antibiotic-resistant bacterial infections or carriage were more common in this older population and notification rates increased over time, particularly for MRSA and VRE. Overall, the population ≥65 years had less notifiable IDs than the younger population. Together with economic evaluations, including the comparison of disability adjusted life-years between diseases, this study should be used to inform public health priorities for the aging population.
Generally, comparing notification rates of IDs can be challenging because of differences in surveillance systems, populations and country-specific infection probabilities as well as changes over time in notification and diagnostic testing policies, healthcare seeking behaviour or better clinical recognition of diseases among older adults, which could mask changes in incidences. Our nation-wide notification data over a broad time-span allowed comparing notification rates in different IDs and age-groups over time, while taking aspects of these challenges into account. Still, the notification rate is not necessarily similar to the true incidence, as some cases never visit healthcare or are not notified. The amount of underreporting may vary between IDs and between age-groups; differential underreporting would induce bias. There are no studies available that estimate the sensitivity and representativeness of the system, but there are no indications for systematic changes in notification in recent years. The fact that the NRR did not change over time for most diseases indicated that age-specific changes in notification policy, testing policy or clinical recognition were unlikely.
Despite differences in surveillance systems across countries, our disease-specific results generally confirm observations in other countries, like the high notification rate of invasive bacterial diseases in the population ≥65 years and the increase in antibiotic-resistant bacteria in recent years. The high notification rate of invasive bacterial diseases is likely to result from the more severe clinical presentation among older adults, rather than more transmission within this population. Older individuals are more prone to develop invasive infections due to immunosenescence, comorbidities, polypharmacy, and/or diminished response to antimicrobial therapy. Delayed recognition of infections due to atypical presentations including the absence of fever in approximately 20% to 30% of older persons with serious infections, leading to a delayed start of therapy, is another reason why invasive disease develops more often in older individuals. As severe infections may lead to functional decline e.g. through exacerbation of underlying health problems, it is important to prevent infections and specifically severe disease in this older population. Risk communication to older people and their caregivers including encouragement to seek healthcare promptly in case of signs of systemic infection can reduce delays in starting therapy. Through vaccination against pneumococcal infections, a large portion of cases with invasive pneumococcal disease may be prevented, as 80% of infections were caused by serotypes included in the recommended 23-valent pneumococcal vaccine. Although vaccination has been available in Norway for those aged ≥65 years since the 1980s, vaccine sales data indicate an uptake of only 15 to 25% (unpublished data NIPH). Prevention of invasive bacterial diseases can also be achieved through prevention of viral respiratory infections due to the increased susceptibility to bacterial super infections during an influenza infection. It is known that the burden of influenza is highest among the older population. We were unfortunately not able to include influenza in our analysis, because of its different surveillance system.
The overall notification rate of IDs was lower in the population ≥65 years compared to the younger population. So, while older people are at higher risk for some IDs, overall they had less notified IDs, specifically, less possible food- and waterborne diseases (except listeriosis), blood-borne diseases/STIs, and (non-invasive) vaccine preventable diseases. Different sexual behaviour, less interaction with the public and reduced travel activity for the population ≥65 years compared to the younger population might explain part of the lower notification rate.
The changes in notification rates over time of invasive pneumococcal disease and pertussis were likely the result of changes in vaccination policy. The decrease in invasive pneumococcal disease coincided with the introduction of pneumococcal vaccination in the childhood immunisation program in 2006 and can be explained by herd protection. The recent decrease in pertussis notifications coincided with the introduction of a booster vaccination at 7 years of age since the school-year 2005–2006. This suggests that the booster not only protects the targeted age-groups, but also provides some protection among older adults. Still, the notification rate of pertussis remains high, suggesting transmission between age groups.
The increase in MRSA and VRE is worrisome, even though the notification rate in Norway is low compared to other countries. It is likely that the MRSA increase resulted not only from a real increase, but also from enhanced surveillance. Nevertheless, the increase in notification of symptomatic infections but not of carriage, supplemented by a time-series analysis of methicillin-sensible and -resistant cases, indicate also a real increase in infections. This increase is likely partly related to increased travelling and the high endemic state of MRSA in other parts of the world as well as increased transmission in Norway. The increase in notified VRE since 2010 was partly due to increased screening, specifically during hospital-based outbreaks. However, a real increase in VRE incidence suggested by the slight increase in the number of cases with a symptomatic VRE infection. The increases in MRSA and VRE notification rates with no change in NRR show that good compliance to infection control measures, screening of at-risk populations, and careful use of antibiotics remain important for all age-groups.
Further exploration of factors that may have caused the disease-specific changes in notification rates showed an increased notification rate of campylobacteriosis acquired in Europe. This might be the effect of increased travelling abroad, which increases the possibility of acquiring travel-related infections. Travel-related salmonellosis, shigellosis, giardiasis and legionellosis increased much less or remained stable. These latter IDs were more often acquired outside Europe (data not shown). The difference between campylobacteriosis and the other travel-related IDs therefore may reflect more travels within Europe. Alternatively, as the change in notification rate in younger age-groups showed similar changes, the increase may reflect increased campylobacter transmission within Europe. The change in tuberculosis resulted from a decrease in notification rate among those born in Norway. This reflects the rapid decrease in tuberculosis incidence in Norway since the late 1940s, as tuberculosis in older adults mainly results from reactivation of previous infections, and fewer Norwegian-born people with a history of tuberculosis are still alive.
Discussion
This study on notification rates of ID and trends over 19 years among the general Norwegian population ≥65 years shows that invasive bacterial diseases, and specifically invasive pneumococcal disease, were most common and occurred more often among older compared to younger individuals. Furthermore, antibiotic-resistant bacterial infections or carriage were more common in this older population and notification rates increased over time, particularly for MRSA and VRE. Overall, the population ≥65 years had less notifiable IDs than the younger population. Together with economic evaluations, including the comparison of disability adjusted life-years between diseases, this study should be used to inform public health priorities for the aging population.
Generally, comparing notification rates of IDs can be challenging because of differences in surveillance systems, populations and country-specific infection probabilities as well as changes over time in notification and diagnostic testing policies, healthcare seeking behaviour or better clinical recognition of diseases among older adults, which could mask changes in incidences. Our nation-wide notification data over a broad time-span allowed comparing notification rates in different IDs and age-groups over time, while taking aspects of these challenges into account. Still, the notification rate is not necessarily similar to the true incidence, as some cases never visit healthcare or are not notified. The amount of underreporting may vary between IDs and between age-groups; differential underreporting would induce bias. There are no studies available that estimate the sensitivity and representativeness of the system, but there are no indications for systematic changes in notification in recent years. The fact that the NRR did not change over time for most diseases indicated that age-specific changes in notification policy, testing policy or clinical recognition were unlikely.
Despite differences in surveillance systems across countries, our disease-specific results generally confirm observations in other countries, like the high notification rate of invasive bacterial diseases in the population ≥65 years and the increase in antibiotic-resistant bacteria in recent years. The high notification rate of invasive bacterial diseases is likely to result from the more severe clinical presentation among older adults, rather than more transmission within this population. Older individuals are more prone to develop invasive infections due to immunosenescence, comorbidities, polypharmacy, and/or diminished response to antimicrobial therapy. Delayed recognition of infections due to atypical presentations including the absence of fever in approximately 20% to 30% of older persons with serious infections, leading to a delayed start of therapy, is another reason why invasive disease develops more often in older individuals. As severe infections may lead to functional decline e.g. through exacerbation of underlying health problems, it is important to prevent infections and specifically severe disease in this older population. Risk communication to older people and their caregivers including encouragement to seek healthcare promptly in case of signs of systemic infection can reduce delays in starting therapy. Through vaccination against pneumococcal infections, a large portion of cases with invasive pneumococcal disease may be prevented, as 80% of infections were caused by serotypes included in the recommended 23-valent pneumococcal vaccine. Although vaccination has been available in Norway for those aged ≥65 years since the 1980s, vaccine sales data indicate an uptake of only 15 to 25% (unpublished data NIPH). Prevention of invasive bacterial diseases can also be achieved through prevention of viral respiratory infections due to the increased susceptibility to bacterial super infections during an influenza infection. It is known that the burden of influenza is highest among the older population. We were unfortunately not able to include influenza in our analysis, because of its different surveillance system.
The overall notification rate of IDs was lower in the population ≥65 years compared to the younger population. So, while older people are at higher risk for some IDs, overall they had less notified IDs, specifically, less possible food- and waterborne diseases (except listeriosis), blood-borne diseases/STIs, and (non-invasive) vaccine preventable diseases. Different sexual behaviour, less interaction with the public and reduced travel activity for the population ≥65 years compared to the younger population might explain part of the lower notification rate.
The changes in notification rates over time of invasive pneumococcal disease and pertussis were likely the result of changes in vaccination policy. The decrease in invasive pneumococcal disease coincided with the introduction of pneumococcal vaccination in the childhood immunisation program in 2006 and can be explained by herd protection. The recent decrease in pertussis notifications coincided with the introduction of a booster vaccination at 7 years of age since the school-year 2005–2006. This suggests that the booster not only protects the targeted age-groups, but also provides some protection among older adults. Still, the notification rate of pertussis remains high, suggesting transmission between age groups.
The increase in MRSA and VRE is worrisome, even though the notification rate in Norway is low compared to other countries. It is likely that the MRSA increase resulted not only from a real increase, but also from enhanced surveillance. Nevertheless, the increase in notification of symptomatic infections but not of carriage, supplemented by a time-series analysis of methicillin-sensible and -resistant cases, indicate also a real increase in infections. This increase is likely partly related to increased travelling and the high endemic state of MRSA in other parts of the world as well as increased transmission in Norway. The increase in notified VRE since 2010 was partly due to increased screening, specifically during hospital-based outbreaks. However, a real increase in VRE incidence suggested by the slight increase in the number of cases with a symptomatic VRE infection. The increases in MRSA and VRE notification rates with no change in NRR show that good compliance to infection control measures, screening of at-risk populations, and careful use of antibiotics remain important for all age-groups.
Further exploration of factors that may have caused the disease-specific changes in notification rates showed an increased notification rate of campylobacteriosis acquired in Europe. This might be the effect of increased travelling abroad, which increases the possibility of acquiring travel-related infections. Travel-related salmonellosis, shigellosis, giardiasis and legionellosis increased much less or remained stable. These latter IDs were more often acquired outside Europe (data not shown). The difference between campylobacteriosis and the other travel-related IDs therefore may reflect more travels within Europe. Alternatively, as the change in notification rate in younger age-groups showed similar changes, the increase may reflect increased campylobacter transmission within Europe. The change in tuberculosis resulted from a decrease in notification rate among those born in Norway. This reflects the rapid decrease in tuberculosis incidence in Norway since the late 1940s, as tuberculosis in older adults mainly results from reactivation of previous infections, and fewer Norwegian-born people with a history of tuberculosis are still alive.
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