In total, 1,630 patients and controls were included in the analyses. Of these, 1,463 (90%) returned a completed questionnaire. A total of 1,086 specimens were collected from patients with diarrhea, 639 in the urban area and 447 in the rural area. From the controls, 544 specimens were collected, 338 specimens in the urban area and 206 specimens in the rural area. The sex and age distribution of the study population is shown in Table 1.
Table 1 Demographic structure of patients and controls, shown as number of probands (percent)
Due to insufficient stool quantities, some samples could not be tested for all viruses and bacteria. Out of 1,630 stool specimens, 1,580 (96.9%) were tested for enteropathogenic bacteria, 1,585 (97.2%) were tested for norovirus, and 1,338 (82.1%) were tested for all four viral agents (Table 2).
Table 2 Detected microorganisms
Incidence of gastroenteritis
The overall incidence of AGE requiring medical consultation was 4,020/100,000 inhabitants (CI95 [1,879; 6,687]), with no significant difference between the urban and rural areas.
Children younger than five years of age had the highest incidence of AGE requiring medical consultation (13,810/100,000; CI95 [6,819; 21,601]), which was significantly different from the rest of the population (P < 0.001, OR = 3.88; CI95 [3.3; 4.6]). In this age group, one out of six children consulted a physician due to AGE in the urban area (15,967/100,000; CI95 [7,979; 24,691]), in contrast to one out of ten children in the rural area (10,791/100,000; CI95 [5,230; 17,368]). This difference was significant (P = 0.008, OR = 1.57; CI95 [1.1; 2.2]). Similarly, in people aged 60 years or older, there was a highly significant difference in incidences between the rural and urban areas (P < 0.001, OR = 2.41; CI95 [1.8; 3.2]) (Table 3).
Table 3 Incidence of AGE per 100,000 inhabitants in different age groups in the study areas
In the urban area, the highest incidences of medical consultations due to AGE were from October through to December, whereas in the rural area, the highest incidences were found in January, March, and April, which is coincident with the different pathogen patterns between the two areas
Incidence of specific viral and bacterial pathogens
A total of 80 out of 1,580 specimens tested positive for enteropathogenic bacteria (72 patients, 6.6%, and eight controls, 1.5%), while 320 out of 1,585 specimens tested positive for a viral agent (280 patients, 17.7%, and 40 controls, 2.5%). Overall, viral and bacterial pathogens were identified in 35% of specimens from patients with AGE (Table 2). Months with high incidences of viral pathogens revealed a higher portion of positive stool specimens than months that showed lower incidences of viral pathogens (Fig. 1).
Norovirus and rotavirus were the most frequently detected pathogens. Norovirus was found in 16% of all cases with AGE (Table 2). The incidence was 626/100,000 inhabitants (CI95 [287; 1,071]). Norovirus was detected all-year-round, with two peaks. The months with the highest incidences of norovirus infection were March and December in the rural area and November and December in the urban area. Morbidity for norovirus-related AGE was 89.2%.
Rotavirus was responsible for 270 episodes/100,000 inhabitants (CI95 [124; 467]). The incidence of rotavirus-related AGE in children younger than five years of age (2,574/100,000, CI95 [1,193; 4,455]) was higher than that for noroviruses in this age group (2,302/100,000, CI95 [1,065; 4,006]), thus, confirming that rotavirus is the most important pathogen causing AGE in young children. Rotavirus-related AGE occurred all-year-round, with a distinctive seasonal peak in March and April. Morbidity for rotavirus-related AGE was 84.1%.
Incidences of AGE due to astroviruses and adenoviruses are shown in Table 2. Children younger than five years were at the highest risk, but astroviruses were an important agent for viral AGE in all age groups. Adenoviruses were rarely detected in patients aged five years or older.
Salmonella was the most frequently detected bacteria found in patients with AGE (162/100,000, CI95 [74; 290]), followed by enterotoxin gene-carrying S. aureus (67/100,000, CI95 [31; 120]) and Campylobacter spp. (55/100,000, CI95 [25; 101]). The age groups with the highest incidences of all of these bacterial agents were children aged 0–14 years. Salmonella infections showed a typical seasonal distribution, prevailing between May and October. Salmonella and Campylobacter spp. showed 100% morbidity.
Aeromonas spp. and Y. enterocolitica had comparable incidences. Plesiomonas spp. and EPEC were found in one and three cases, respectively (Table 2). EaggEC, EHEC, EIEC, ETEC, or Shigella spp. were not isolated.
A total of 34 positive stool specimens from patients were carrying two or more infectious agents (Table 4). In controls, no co-infections were detected.
Table 5 shows the typical symptoms of AGE caused by the various viral (frequently vomiting) and bacterial (frequently fever) enteropathogens. Table 6 shows the risk factors for acquiring AGE.
Table 5 Self-reported symptoms of patients
Table 6 Factors associated with a higher risk for acquiring AGE based on multiple logistic regression (P-value, OR)