Older adults (aged ≥65 years) are more susceptible than younger adults to certain enteric infections such as invasive Campylobacter and Salmonella [1,2]. Illness among older adults is also more likely to be severe, leading to hospitalization, long-term complications, or death [3–7]. Several age-related factors may contribute to older adults’ increased susceptibility and disease severity, including weakening of the immune system, changes to the gastrointestinal tract, higher prevalence of comorbid conditions, and more frequent use of antacids and immunosuppressants [1,8]. The rates of gastrointestinal hospitalizations and deaths are highest among older adults [3,5,9,10]. In the United States, the overall burden of nontyphoidal Salmonella in adults aged ≥65 years was estimated at 110,100 illnesses annually, resulting in 5,100 hospitalizations, and 220 deaths (296, 13 and 0.59 per 100,000, respectively). Campylobacter caused an estimated 110,200 illnesses annually, resulting in 3,200 hospitalizations, and 60 deaths (296, 9 and 0.16 per 100,000, respectively) [5]. In Canada, nontyphoidal Salmonella causes an estimated 534 hospitalizations and 27 deaths annually (11 and 0.29 per 100,000, respectively) among adults aged ≥60 years [9].

The rapid diagnosis of enteric infections in older adults can improve outcomes by providing timely and appropriate treatment. However, the early detection of enteric infections in older adults is challenging because typical signs and symptoms of disease may be less common or absent in this age group [11,12]. For example, episodes of vomiting and abdominal pain have been reported less frequently among older adults with viral gastrointestinal illness compared with younger adults [13]. Fever is also less common in older adults with a gastrointestinal infection [14]. Moreover, pre-existing conditions and comorbidities can make the diagnosis of an enteric infection more challenging. For example, it may be difficult to determine whether diarrhea, nausea, or vomiting is caused by an enteric infection or a non-infectious cause [15].

Understanding the clinical signs and symptoms among older adults with enteric infections could improve the timeliness and accuracy of clinical diagnoses, thereby improving patient outcomes and increasing the number of cases diagnosed and reported to surveillance. The aim of this study was to describe clinical characteristics by age among cases with culture-confirmed Campylobacter and nontyphoidal Salmonella infections and acute gastroenteritis using data from surveillance and epidemiological studies conducted in Australia, Canada, and the United States.

Data were available for 3,702 cases with a culture-confirmed Campylobacter infection (545 in Australia, 1,846 in Canada, and 1,311 in the United States); 2,736 with a culture-confirmed nontyphoidal Salmonella infections (111 in Australia, 1,337 in Canada, and 1,288 in the United States); and 6,876 people reporting an episode of acute gastroenteritis (792 in Australia, 548 in Canada, and 5,536 in the United States) (Table 1).

Across the three countries, the percentage reporting each symptom was similar by age group for Salmonella, Campylobacter, and acute gastroenteritis (Figures 1–3, Supplementary Information). In each country, there was a negative linear correlation between the percentage of symptoms reported and increasing age group. Conversely, a positive linear correlation was consistently observed between the percentage of cases hospitalized and increasingly older age groups (Figures 1–3, Supplementary Information). There was no significant difference between the slopes for each pathogen, so study data from the three countries were pooled.

The percentage reporting each symptom was similar among those with culture-confirmed Campylobacter and Salmonella infection. Most Campylobacter and Salmonella cases reported abdominal cramps (85% and 84%, respectively) and fever (74% and 76%). The percentage reporting bloody diarrhea was similar for Campylobacter (39%) and Salmonella (40%); vomiting was reported in 31% and 42% of cases, respectively. The median duration of illness was six days for Campylobacter and seven days for Salmonella (US cases only). Only 10% of Campylobacter cases were hospitalized for their illness (all sites), for a median of three days (US only) (Figure 1), compared with 20% of Salmonella cases for a median of seven days (Figure 2). The percentage of acute gastroenteritis respondents reporting symptoms was lower for all symptoms compared with culture-confirmed cases, ranging from 3% for bloody diarrhea to 60% for abdominal cramps (Table 2). The median duration of illness was two days (US only) and 2% were hospitalized (all sites) for a median of three days (Canada only) (Figure 3).

There was a significant negative correlation between symptoms and increasing age, except for bloody diarrhea in acute gastroenteritis (Table 2). For Salmonella and Campylobacter infections, there was a negative linear correlation between bloody diarrhea and age group; ranging from 59% and 55% for Campylobacter and Salmonella cases, respectively, in those aged <5 years, to 9% and 4%, respectively, in those aged ≥85 years. For both pathogens, the percentage reporting abdominal pain or cramps, fever, and vomiting was higher in persons aged 5–24 years than <5 years. The percentage reporting vomiting was similar across age categories (Table 2, Figures 1 and 2). For acute gastroenteritis, abdominal cramps were reported more frequently in persons aged 5–24 years compared to all other age groups. Fever and vomiting declined linearly with age, though less so in acute gastroenteritis. For all symptoms, reporting percentages plateaued among persons ≥65 years with acute gastroenteritis (Table 2, Figure 3). Among hospitalized US Salmonella and Campylobacter cases, there was a similar negative correlation between age group and bloody diarrhea, abdominal cramps, fever, and vomiting (Table 2).

There was a positive correlation between hospitalization and increasing age group, ranging from 7% among those aged <5 years to 48% among those aged ≥85 years for Campylobacter and 17% to 49% for Salmonella, respectively (Table 2, Figures 1 and 2). A similar trend was observed among those reporting acute gastroenteritis, ranging from 1% in those aged 5–24 years to 17% in cases aged ≥85 years (Table 2, Figure 3). Duration of hospitalization increased with age for Campylobacter and Salmonella, whereas duration of illness was more similar across age groups. Additional symptoms, including chills, headache, muscle pain, and nausea, were consistent across age groups. Dehydration increased with age in Campylobacter cases. Chronic gastrointestinal illness diagnosis or symptoms increased with age in Campylobacter and acute gastroenteritis. Antibiotic use was consistent across age groups, and PPI use increased with age for Campylobacter and Salmonella cases (Supplementary Information Table 1). Percentage missing for symptoms and hospitalization was consistent across age groups (Supplementary Information Table 2).

This study describes symptoms by age among persons with culture-confirmed Campylobacter and nontyphoidal Salmonella infections and acute gastroenteritis using data from surveillance and epidemiological studies conducted in Australia, Canada, and the United States. Whereas other studies have described the burden and severity of acute gastroenteritis by age [5,34], differences in reported symptoms by age group have not systematically been described. Although older adults are more likely to have severe illness and be hospitalized, this study found that the percentage reporting symptoms typically associated with enteric infections decreases with age. This has important implications for clinical diagnosis, treatment, and public health research.

Among persons with culture-confirmed Campylobacter and nontyphoidal Salmonella and acute gastroenteritis, older age groups were less likely than other adults and children to report classical gastrointestinal symptoms, including bloody diarrhea, abdominal pain or cramps, vomiting, and fever. Bloody diarrhea, which is often used as a marker for more severe illness in studies that estimate the number and human health impact of foodborne and enteric diseases [35–37], had the largest range between the youngest and oldest age groups (~50% for Campylobacter and Salmonella cases). Fever, a key diagnostic criteria and predictor of treatment and severity, was also significantly lower in older adults. Previous studies have reported that older adults with gastrointestinal illness are less likely than other adults to report symptoms such as abdominal cramps, fever, and myalgia [15,38]. Moreover, objectively measured fever may be absent or blunted in older adults with infections [39].

Despite fewer reported symptoms, our results show that hospitalization rates increased with age. This finding is consistent with other studies that have found an increase in invasive infection, hospitalization, length of hospitalization, and mortality with age [3–5]. Among those hospitalized, the percentage reporting symptoms remained lower among older adults compared with younger adults and children. This suggests that more older adults present with severe illness requiring hospitalization in the absence of fever or bloody diarrhea or other symptoms typically associated with severe illness. Alternatively, clinicians may be more likely to hospitalize older adults for other reasons, such as dehydration. Previous studies have found an association between PPI use and an increased risk of hospitalization with gastrointestinal infections [40]. We found that PPI use increased with age.

Among those hospitalized, length of hospitalization was of longer duration among older people compared with their younger counterparts although a longer overall duration of illness was not observed in older adults. Older adults are more likely to experience complications from gastrointestinal illness, including septicemia, meningitis, acute renal failure, hemolytic uremic syndrome, arrhythmias, and Guillain-Barré syndrome [41], which may account for the longer duration of hospital stays. Some previous studies have found other pathogens, such as norovirus, have a longer illness duration in older adults [42,43].

This study found that older adults were more likely than younger adults and children to report dehydration associated with Campylobacter, but our evidence was limited because dehydration was only collected in Canada. However, other studies have also reported older adults may be at increased risk for dehydration and its complications, including electrolyte imbalance, delirium, falls resulting in bone fractures, hypertension, and prolonged infection. So, although infectious diarrhea may be more difficult to diagnose in older adults, close observation and fluid therapy for diarrhea are merited [15].

Without typical signs and symptoms, gastrointestinal infections may be underdiagnosed or misdiagnosed. The symptoms of infectious diarrhea are similar to other ailments common in older adults, including fecal incontinence, fecal impaction with overflow, laxative use, irritable bowel syndrome, or drug-induced diarrhea [41], and infections can present with different symptoms in older adults, such as falls, delirium, anorexia, or generalized weakness [12], which can be exacerbated by cognitive impairment [44]. In a review of Escherichia coli O157:H7 outbreaks in LTCF, one study concluded that with bloody diarrhea as the sole complaint, and in the absence of fever and pain, cases were initially misdiagnosed as hemorrhoids or diverticulosis [45]. Categorizing severe illness is an important and challenging aspect of estimating the overall burden of gastroenteritis. Previous estimates used bloody diarrhea as an indicator of severe illness [32,36,37] and assumed the percentage of severe illness was similar to the general population [5]. Given the results found in this study, it is likely that bloody diarrhea alone is not a good measure of severity when estimating the burden of gastrointestinal illness in older adults.

This study is subject to several limitations. First, the data were from three countries spanning different time periods, and studies used different methodologies. All three countries used the same case definition to extract data. However, Canadian surveillance included LTCF residents, sporadic, outbreak- and travel-associated cases, which were included in the analysis to increase case numbers. By design, US and Australian case-control studies excluded these groups. Despite these differences, this study found high concordance for symptoms regardless of country, time, and the serotype causing infection. Second, hospitalization and duration of hospitalization were used as indicators of severity, however clinicians may be more likely to hospitalize older adults, even if the symptoms and signs of illness are of the same severity as someone younger. In addition, after an older person is admitted to the hospital, there may be a higher likelihood of diagnosing and testing for gastroenteritis. There may have been similar biases with young children, as there are different treatment and management recommendations and practices. Third, this study was unable to distinguish between older adults in LTCF, who were excluded from most studies, and those living in the community, and there are important differences between these populations. Fourth, symptom information was based on self-report. Fifth, although missingness of symptom and hospitalization was consistent by age group, it may have been more challenging to enroll older adults with more severe illness, or there could have been age-specific differences in interviews. Finally, this study is subject to the inherent limitations of epidemiological case-control studies, cross-sectional surveys, and surveillance systems. Moreover, while the case-control studies and surveillance included only culture-confirmed cases, cross-sectional surveys include self-reported illnesses, which may or may not have been diagnosed.

This study demonstrated older adults consistently report fewer symptoms across multiple studies from three countries, despite evidence from previous studies showing older adults are more susceptible to enteric infections and more likely to be hospitalized and experience severe outcomes. As the population ages, it is important to understand the clinical presentation of gastrointestinal illness in older adults to prioritize early recognition and rapid treatment to prevent hospitalizations and poor outcomes. This study highlights the importance and challenges of early clinical detection of gastrointestinal illness in older adults and the need for research on age-specific risk factors, symptoms, and severity indicators associated with gastrointestinal illness.