Arboviral Infections in the Elderly: A Brazilian Study

ABSTRACT

INTRODUCTION: The elderly have specific health needs, such as greater attention to emerging and reemerging infections. Arboviruses, Dengue (DEN), Zika (ZIK) and Chykungunya (CHIK), appear periodically with a morbidity and mortality that affects many elderly people.

OBJECTIVE: Describe the demographic, clinical and epidemiological profile of confirmed cases of DEN, ZIK and CHIK in elderly people in a municipality in the eastern region of Minas Gerais, from 2015 to 2017.

METHODS: Study with a quantitative, observational and descriptive approach using secondary data from the Notifiable Diseases Information System.

RESULTS: A total of 1,434 cases of DEN, 1,844 of CHIK and 206 of ZIK were reported. The cumulative incidence was 635, 1,222.5 and 49.3 respectively. The age group of 60-69 years old, female, brown skin were the most affected. For DEN and ZIK there were no recorded deaths. For CHIK, there were 11 deaths with a lethality of 0.3% to 3.4% depending on the age group. The epidemiological-clinical confirmation criterion was the most used. Most reported symptoms: arthralgia, fever, myalgia and headache. As for the completeness of the data, 28 variables were analyzed. For DEN 11% was very bad or bad, 68% good and 18% excellent. For CHIK, 11% very bad or bad, 89% excellent. For ZIK, 22% very bad and 78% excellent.

CONCLUSION: Predominant clinical-epidemiological profile between 60-69 years old, female and race / brown skin. There is an important gap in the information, which makes a better study about this population impossible.

KEYWORDS: Arbovirus Infections; Information system; Elderly

INTRODUCTION

Demographic transition in Brazil has occurred rapidly over recent decades, resulting in a process of population aging. The country’s epidemiological transition scenario draws attention due to the significant impact of communicable diseases on the population, many of which are neglected diseases. In 2015, older adults accounted for 10% of the total population in Brazil.¹ This population has specific health needs, not only with regard to chronic diseases, but also in relation to emerging and re-emerging infections.² Among these diseases, arboviral infections stand out. These are diseases caused by ecologically well-defined viruses (arboviruses), whose transmission occurs through hematophagous arthropods.³ Currently, the main arboviral diseases affecting older adults are chikungunya (CHIK) and Zika (ZIK), in epidemic form, and dengue (DEN), often in endemic form.⁴

DEN is an acute febrile infectious disease transmitted by a vector, most commonly the mosquito Aedes aegypti. Infection by the virus in humans can lead to a wide spectrum of clinical manifestations, ranging from mild fever to dengue shock syndrome, which is potentially fatal.⁴ In Brazil, dengue is present endemically in all states, with particular emphasis on the epidemics of 2015 and 2016, with 1.6 million and 1.5 million cases, respectively.⁵

Like DEN, the ZIK virus is also transmitted by the mosquito Aedes aegypti,⁵ but it can also be transmitted through other routes, such as sexual, vertical, and blood transmission.⁶ These two arboviral diseases, together with CHIK, share similar clinical characteristics, varying in the intensity of signs and symptoms such as arthralgia, swelling of the extremities, moderate fever, headache, non-purulent conjunctivitis, dizziness, myalgia, and gastrointestinal disorders, which may last approximately 4 to 7 days.⁵˒⁷ Evident since 2016, when a high number of newborns presented with microcephaly following maternal infection during pregnancy,⁶ ZIK has demonstrated neurotropic activity, enabling it to cross the fetal blood–brain barrier, bind to neuronal cells in the brain, and subsequently induce apoptosis and interfere with neuronal development, proliferation, and migration.⁸

In CHIK infection, approximately 75% of individuals present with the symptomatic form of the disease, a significant proportion compared with other arboviral infections.⁴ The acute phase of the disease begins abruptly soon after the incubation period, with high fever, intense arthralgia/arthritis, and maculopapular rash, which usually appears two to five days after the onset of fever.⁴˒⁹ In addition, joint pain may persist, characterizing the subacute phase, which can last up to three months or progress to the chronic phase of the disease, with the development of disabling chronic arthropathy, thereby compromising the quality of life of affected individuals.⁴˒⁹

The emphasis on older adults is due to their vulnerability to developing more severe forms of these viral infections.⁴ There is evidence in the literature of worsening signs and symptoms of DEN infection in older adults,¹⁰ as well as increased rates of dengue hemorrhagic fever and dengue shock syndrome in this population.¹¹ A high proportion of hospitalizations¹² and infections associated with hospitalization¹¹ have also been reported. With regard to CHIK, specifically in the older population, joint pain, edema, and prolonged fever are more predominant.¹³ Studies indicate that, in older adults, CHIK fever is more prevalent in the chronic phase of the disease, with some cases progressing to atypical forms.¹⁴

Regarding ZIK virus infection, there is evidence that the virus may be associated with Guillain–Barré syndrome, a condition characterized by generalized weakness and paralysis, particularly among older adults.¹⁵ It is believed that the predominance of negative outcomes in this population is attributed to factors such as the high number of pre-existing comorbidities and age-related decline in organic reserve and immune function, predominantly affecting cellular and humoral immunity, with impaired cytokine responses.¹¹

Considering the significant epidemiological context of arboviral disease occurrence in Brazil in recent years, the complex clinical manifestations in the older population, and the limited number of scientific studies related to the epidemiology of DEN, ZIK, and CHIK in individuals aged 60 years or older in the country, the present study aimed to describe the demographic, clinical, and epidemiological profile of confirmed cases of DEN, ZIK, and CHIK among older adults in a municipality in the eastern region of Minas Gerais, Brazil, from 2015 to 2017.

MATERIALS AND METHODS

According to data from the Brazilian Institute of Geography and Statistics (IBGE), the municipality of Governador Valadares, located in the eastern region of the state of Minas Gerais (MG), has a territorial area of 2,342.325 km², as determined in 2018.¹⁶ Projections from the Brazilian Ministry of Health estimate that in 2020 the municipality had 281,046 inhabitants, of whom 147,619 (52.5%) were female; 27.1% of the general population were aged 19 years or younger, and 16.2% were aged 60 years or older.¹⁷ The municipality has a Municipal Human Development Index (MHDI) of 0.727, according to the United Nations Development Programme (UNDP). Regarding income, longevity, and education, the MHDI values are 0.714, 0.834, and 0.644, respectively.¹⁸ Governador Valadares is the largest municipality in the eastern region of Minas Gerais in terms of population.

A quantitative, observational, descriptive study was conducted of probable cases (confirmed and suspected) of arboviral diseases (DEN, ZIK, and CHIK) in individuals aged 60 years or older, recorded in the Information System for Notifiable Diseases (SINAN-Net) of the Health Surveillance Department of the Municipal Health Secretariat of Governador Valadares. The study period was from January 1, 2015 to December 31, 2017, and case records were classified according to their underlying cause of illness, based on the 10th Revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-10), using codes A90 (Dengue), A92.0 (Chikungunya fever), and A92.8 (Zika virus disease).

All probable cases of DEN, ZIK, and CHIK reported during the study period were included. Probable cases were defined as those with laboratory or clinical-epidemiological confirmation. Records of discarded cases and those with incomplete study variables were excluded.

The following variables from the notification forms were analyzed: general data (municipality and date of notification); individual notification data (date of birth, age, sex, race/skin color, and educational level); residence data (municipality, district, neighborhood, and area of residence); epidemiological background and clinical data (signs and symptoms, hospitalization, and clinical outcome); case classification data (criteria for confirmation or exclusion of diagnosis); and final classification. For the race/skin color variable, the categories defined by IBGE were used: White, Black, Brown, Yellow, and Indigenous. The choice of age group strata (60–69, 70–79, and ≥80 years) was based on different stages of later life, as well as similarities in morbidity and mortality profiles.

Point incidence rates (LapSCA) were calculated for each study year, using as the numerator the total number of cases that occurred in the year multiplied by 100,000 inhabitants, and as the denominator the estimated resident population aged 60 years or older for the same period.

Due to difficulties in obtaining the number of individuals exposed to the risk of arboviral infection in Governador Valadares, the resident population of the municipality was used. Data on the resident population were obtained from the Department of Informatics of the Unified Health System (DATASUS), based on IBGE estimates. Cumulative incidence rates and case fatality rates were also calculated.

For cumulative incidence, the numerator consisted of the total number of new cases occurring between 2015 and 2017 multiplied by 100,000 inhabitants, and the denominator was the total resident population aged 60 years or older during the same period. Case fatality was calculated as the proportion of deaths from each disease among the total number of cases in the study population, per year, multiplied by 100.

Data analysis was performed using descriptive statistical methods, including analysis of frequencies, proportions, and means of categorical and numerical variables. The software programs EpiInfo™ version 7.2 and Microsoft Excel® were used to generate figures and tables.

The evaluation of the completeness of essential variables for understanding the epidemiology of arboviral diseases aimed to identify variables with incomplete, blank, or ignored information in the notification forms.¹⁹ Incompleteness was assessed using a scale proposed by Santos (2012): excellent (<5%); good (5–10%); regular (11–20%); poor (21–50%); and very poor (≥51%).¹⁹

In the present study, review by a Research Ethics Committee was waived, as the study used secondary, non-nominal, publicly available data, in accordance with Brazilian National Health Council Resolution No. 510/2016. However, the researchers strictly adhered to international ethical standards for research involving human subjects and to National Health Council Resolution No. 466/2012.²⁰

RESULTS

A total of 3,484 cases of arboviral diseases in individuals aged 60 years or older were reported in Governador Valadares, including 1,434 cases (41.1%) of dengue (DEN), 1,844 cases (52.9%) of chikungunya (CHIK), and 206 cases (5.9%) of Zika (ZIK). Of these, 2,243 cases (64.3%) were confirmed by laboratory testing or clinical–epidemiological criteria, comprising 747 cases (33.3%) of DEN, 1,438 cases (64.1%) of CHIK, and 58 cases (2.5%) of ZIK. A total of 11 deaths were recorded during the study period, all of which were confirmed cases of CHIK, resulting in a case fatality rate of 0.7%.

The cumulative incidence rates of arboviral diseases during the study period were 635 cases per 100,000 inhabitants for DEN, 1,222.5 cases for CHIK, and 49.3 cases for ZIK. The highest point incidence rates were observed in 2017 for DEN (1,835 cases per 100,000 inhabitants) and CHIK (3,532.4 cases), and in 2016 for ZIK (148 cases). Regarding the month of symptom onset, the highest number of reported cases occurred during the first quarter of each year studied. DEN and ZIK cases peaked in February, presenting the highest incidence rates (345.1 cases per 100,000 inhabitants for DEN and 27.2 cases for ZIK). For CHIK, March stood out with a relatively high incidence rate (651.2 cases).

With respect to age, the highest frequency of cases was observed in the 60–69-year age group for all three arboviral diseases, accounting for 33.2% (477) of DEN notifications, 44.5% (821) of CHIK cases, and 21.8% (45) of ZIK cases. The mean age was 78 years for DEN (range: 60–96 years), 84 years for CHIK (range: 60–108 years), and 71.5 years for ZIK (range: 60–83 years) (Table 1). The highest incidence rates were also recorded in the 60–69-year age group for all three arboviruses (DEN = 752.4; CHIK = 1,295; ZIK = 70.9). However, no deaths were recorded for DEN or ZIK. For CHIK, the case fatality rate by age group was 0.3% among individuals aged 60–69 years, 0.7% among those aged 70–79 years, and 3.4% among those aged 80 years or older.

Table 1. Dengue, Chikungunya, and Zika virus cases according to sex, age group, symptomatology, and comorbidities in Governador Valadares, 2015–2017.

Regarding the remaining sociodemographic variables, most cases occurred among females (67.1%). When stratified by type of arboviral disease, this distribution included 493 cases of DEN (57.7%), 966 cases of CHIK (66.0%), and 48 cases of ZIK (Table 1). With respect to race/skin color, a higher frequency was observed among older adults classified as Brown for DEN (34.0%; n = 254) and CHIK (29.7%; n = 428). Among ZIK cases, individuals classified as White and Brown accounted for the same number of cases (n = 13 each). Most notifications occurred among residents of urban areas, with frequencies of 90.4% (n = 774) for DEN, 94.2% (n = 1,380) for CHIK, and 94.8% (n = 55) for ZIK. The educational level variable showed a high degree of incompleteness for all three arboviral diseases.

Clinical–epidemiological criteria were the most frequent confirmation method for all arboviral diseases, accounting for 71.1% (n = 609) of DEN cases, 84.3% (n = 1,234) of CHIK cases, and 100% (n = 58) of ZIK cases. Regarding clinical variables, DEN and CHIK shared four of the five most frequently reported signs and symptoms: arthralgia (39.6% in DEN and 93.0% in CHIK), fever (67.2% in DEN and 88.1% in CHIK), myalgia (66.3% in DEN and 80.4% in CHIK), and headache (44.8% in DEN and 59.0% in CHIK). In addition, vomiting was reported in 11.8% of DEN cases, while back pain was reported in 28.9% of CHIK cases. The ZIK notification form does not include signs and symptoms as variables to be completed; therefore, this arboviral disease could not be analyzed with regard to these clinical variables.

With respect to pre-existing conditions, individuals affected by DEN presented hypertension in 8.3% of cases and diabetes mellitus in 2.0%, whereas those affected by CHIK presented hypertension in 18.5% and diabetes in 6.7% of cases. The ZIK notification form does not include information on comorbidities.

Regarding data quality in the notifications of the three arboviral diseases, field completeness analysis was performed using 28 key variables for DEN and CHIK, which are included in the same notification form. For ZIK, which does not have a specific notification form, nine key variables from the general notification form were analyzed.

For DEN, only three variables (10.7%) were classified as having poor or very poor completeness, with missing information mainly related to educational level, race/skin color, and hospitalization. Clinical outcome was classified as having regular completeness. Nineteen variables (67.8%), primarily related to patient symptomatology, were classified as having good data quality, and only five variables (17.8%) were classified as excellent, particularly those related to neighborhood of residence, age, and sex (Table 2).

Table 2. Analysis of incompleteness of variables recorded in Dengue, Zika, and Chikungunya notification forms in Governador Valadares, from 2015 to 2017.

Assessment scale: excellent (<5%); good (5–10%); fair (11–20%); poor (21–50%); and very poor (>51%).Source: SINAN-Net / Health Surveillance Department / Municipal Health Secretariat of Governador Valadares.

For CHIK, three variables (10.7%) were classified as having poor or very poor completeness, namely race/skin color, educational level, and hospitalization. The remaining 25 variables (89.2%) were classified as excellent in terms of data completeness.

For ZIK, two variables (22.2%) were classified as having very poor completeness—educational level and race/skin color—while the other seven variables (77.7%) were considered to have excellent completeness (Table 2).

DISCUSSION

Urban arboviral diseases transmitted by the mosquito Aedes aegypti have become major challenges for public health actions, both in terms of surveillance and in the care of clinically moderate and severe patients.⁹ The Zika virus and chikungunya fever virus can be highlighted, as they caused significant epidemic processes in Brazil starting in 2015. During the study period, the state of Minas Gerais (MG) experienced outbreaks of dengue (DEN), Zika (ZIK), and chikungunya (CHIK). The city of Governador Valadares was one of the most affected, especially with regard to CHIK, which in 2017 alone resulted in more than 11,000 reported cases.

The scientific literature is scarce regarding epidemiological studies involving the population aged 60 years or older and the epidemiology of arboviral diseases. In Governador Valadares, the arboviral disease profile in this population is concerning, given the clearly high morbidity rates, as well as the relevant lethality observed for CHIK.

According to the Brazilian Ministry of Health, between 2015 and 2017, 3,447,832 probable cases of DEN were reported nationwide, of which 10.7% occurred in individuals aged 60 years or older.²² For CHIK, in 2017 Brazil recorded 185,593 probable cases between epidemiological weeks 1 and 52, with 15.5% occurring in older adults.¹⁷ Regarding ZIK virus, autochthonous transmission was confirmed in the country from April 2015 onward,²³ and between 2015 and 2017, 229,340 probable cases were reported nationwide, with older adults accounting for just over 19,000 cases (8.5%).²² Epidemiological bulletins from the Ministry of Health do not provide analyses stratified by age group, highlighting the need for more in-depth epidemiological and clinical studies according to the life cycle.

For Minas Gerais, the State Health Secretariat (SES-MG) provides public data for DEN and CHIK through its Surveillance Portal. During the same study period, the state reported 625,087 cases of DEN, of which 10.4% occurred in individuals aged 60 years or older. For CHIK, 14,144 probable cases were reported in 2016 and 2017, with 17.2% occurring among older adults. Notably, between 2015 and 2017, the municipality of Governador Valadares alone accounted for 63.0% of all CHIK cases in the state.²⁴

According to data from the Ministry of Health and the State Health Secretariat of Minas Gerais for Governador Valadares, between 2014 and 2019, 930 cases of DEN were reported in older adults, representing 6.4% of all cases. For ZIK, between 2016 and 2018, individuals aged 60 years or older accounted for 3.3% of cases (28 probable cases), while for CHIK in 2017, this proportion reached 16.3% (1,411 cases). The results of the present study indicate a higher incidence of CHIK, followed by DEN and ZIK, among older adults in Governador Valadares.²²˒²⁴ These proportions are consistent with the age distribution patterns observed at both the national and state levels.

During the study period, 11 deaths due to arboviral diseases were identified, all of which occurred in 2017 and were caused by complications related to CHIK. In that year, 13 deaths due to CHIK were recorded in the state of Minas Gerais, of which 11 occurred among older adults in Governador Valadares.²⁴ These deaths affected older individuals with comorbidities and occurred mainly during the first quarter of the year, coinciding with the period of highest disease incidence. Thus, in addition to representing a significant proportion of CHIK cases, older adults also constitute the population at highest risk for severe outcomes and death.²⁵

A higher number of reported cases was observed during the first quarter of all study years, corresponding to the summer season, when increased temperatures can influence vector populations by shortening larval development time and consequently increasing the adult mosquito population. Additionally, higher temperatures reduce the extrinsic incubation period, allowing viruses to reach the mosquito’s salivary glands more rapidly, thereby enabling transmission in a shorter time frame.²⁶

With regard to age groups, higher arboviral incidence was observed among individuals aged 60–69 years, which is consistent with Brazil’s population age distribution, as this subgroup represents the largest proportion within the older population.² Similar findings have been reported in other scientific studies.²⁶

Regarding race/skin color, this study showed that most probable cases occurred among individuals classified as Brown, a finding corroborated by studies conducted in the northeastern region of Brazil.²˒²⁷ Demographic transition, characterized by increased life expectancy and population aging—particularly among Black and Brown populations—has occurred alongside marked socio-spatial inequalities. These inequalities result in vulnerabilities related to environmental susceptibility to arboviral transmission, such as precarious housing conditions and lack of adequate sanitation.²⁷

The predominance of DEN cases among females (67.1% of notifications) has been reported in other Brazilian cities.²⁸˒²⁹ Higher arboviral incidence among women may be related to sociocultural factors, including lower health service utilization by men and greater time spent by women in domestic environments, where mosquito breeding sites are commonly found.²⁵˒²⁶˒³⁰

Regarding place of residence, most notifications occurred among urban residents. According to the 2015 National Household Sample Survey (PNAD), 84.7% of the Brazilian population lives in urban areas.³¹ In addition, intense rural-to-urban migration since the 1960s, combined with infrastructural factors such as hygiene and sanitation conditions—closely linked to socioeconomic status—has led to unequal impacts on communities, with poverty being strongly associated with arboviral transmission.³⁰ The increase in potential breeding sites for the primary vector has contributed to the urbanization of Aedes aegypti, largely explaining the high number of urban cases.³²

Regarding clinical manifestations, fever, arthralgia, myalgia, and headache were the most frequently reported symptoms among older adults with DEN and CHIK. A study conducted in the state of São Paulo² found that 97.0% of patients with arboviral diseases presented fever, 78.8% myalgia, and 75.8% intense arthralgia. Other studies conducted in Governador Valadares and in Rio Grande do Sul, encompassing all age groups, reported fever, headache, and myalgia as the most common symptoms, indicating consistency between symptom profiles in the general and older populations.³³˒³⁴

Another variable consistent with the literature was the presence of underlying diseases among older adults with arboviral infections, with diabetes mellitus and systemic arterial hypertension being the most prevalent. These findings align with studies involving older populations and with the Brazilian epidemiological profile, in which hypertension ranks first and diabetes third among the most prevalent chronic non-communicable diseases.³⁵

Regarding diagnostic confirmation criteria, the Ministry of Health recommends laboratory confirmation whenever possible. However, due to limited laboratory capacity within the Unified Health System to respond to public health emergencies such as DEN, ZIK, and CHIK outbreaks in Minas Gerais during the study period, clinical–epidemiological criteria predominated. According to Ministry of Health guidelines, expanding rapid laboratory response capacity is essential to confirm or rule out cases whenever feasible.³⁶

The completeness analysis of essential variables highlighted deficiencies particularly in educational level, race/skin color, and hospitalization data. This may reflect insufficient training or lack of attention by health professionals responsible for notification and data recording, despite the importance of demographic and clinical variables for accurate morbidity and mortality analyses based on health information systems.³⁷

Study limitations include the use of secondary data, a high proportion of incomplete fields for certain variables, and the inability of notification forms to capture other relevant health-related factors. Additionally, although the data allowed characterization of the clinical and demographic profile of DEN, CHIK, and ZIK among older adults, many cases were classified based on clinical–epidemiological criteria rather than laboratory confirmation. While health information systems are widely used for decision-making, ensuring data completeness and quality is essential for evidence-based interventions. Another important limitation is the scarcity of studies addressing the epidemiological profile of arboviral diseases in individuals aged 60 years or older.

CONCLUSION

Knowledge of the clinical and epidemiological profile of older adults affected by arboviral diseases expands understanding of infectious diseases in this population. The quality of completion of variables in arboviral disease notification forms represents an important limitation for the development of public health policies, making it necessary to implement strategies to improve the completeness of these fields. Nevertheless, the overall quality of these data must also be emphasized.

It is evident that arboviral diseases in the older population constitute a topic that warrants extensive investigation, particularly in light of the chikungunya-related case fatality observed in Governador Valadares. Such efforts are essential to mitigate atypical or severe clinical manifestations in individuals aged 60 years or older, given the higher risks associated with aging and the need for specific clinical management. Furthermore, deeper scientific investigation of this topic will help address gaps related to health promotion, prevention, and maintenance for this population affected by arboviruses.

ACKNOWLEDGMENTS

We thank the Municipal Health Secretariat of Governador Valadares – Epidemiology Management Division, for providing the non-nominal database on Dengue, Zika, and Chikungunya.

CONFLICT OF INTERESTS

The authors declare that there were no conflicts of interest in the development of this study.

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