Clinical and epidemiological characteristics of the study participants
There were 1,799 individuals with a serology test result (positive or negative) during the study period; 42% of cases were positives for SARS-CoV-2 (anti-SARS-CoV-2 IgM, IgG, or IgM+IgG seropositivity), and 58% of them were negative (Table 1). Seropositive cases were older than those seronegative (p = 0.0001): median 37 (IQR: 28-49) years old vs. 34 years (IQR: 25-46), respectively. From the 703 seropositive cases and 979 seronegative cases with information on age, the age range of seropositive cases was dominantly 21-30 years old (27.03%), followed by the group of 31-40 years old (26.74%); this finding was statistically different from what was observed in seronegative cases (p = 0.002).
A higher proportion of seropositive (58.99%) and seronegative (56.57%) individuals were women. Moreover, most of the individuals (seropositive or seronegative) reported a previous record of vaccination against influenza (>50%). Regarding comorbidities, overweight was the most prevalent in both study groups (19.84% in seropositive cases and 17.35% in those seronegative, p= 0.304); however, diabetes was most prevalent in seropositive cases in comparison with those seronegative (9.39% vs. 5.56%, respectively, p= 0.002). Seropositive cases declared more symptoms than those seronegative (mean ± SD: 4.489 ± 2.409 vs. 3.810 ± 2.423, respectively, p = 0.008).
Blood type did not show differences between both study groups (p = 0.403). On the other hand, seropositive cases declared less knowledge about having contact with a patient with COVID-19 before undergoing the serological test (seropositive cases 67.20% vs. seronegative cases 73.63%, p = 0.003). However, seropositive cases had more days of contact with COVID-19 patients pre-test (median 12 days [IQR: 7-17] vs. 10 days [IQR: 6-15], respectively, p= 0.0023). In both study groups, the contact with SARS-CoV-2 suspects was at home (46.56% in seropositive cases, and 47.17% in seronegative cases, p = 0.798, data not shown).
Table 1. Demographic characteristics, comorbidities, and risk contacts of individuals negative or positive to anti-SARS-CoV-2 antibodies
Variables
|
Positive for anti-SARS-CoV-2 antibodies
|
Negative for anti-SARS-CoV-2 antibodies
|
P-valuea
|
N=756
|
N=1043
|
|
Age (years) Median (P25th-P75th)
|
37 (28-49)
|
34 (25-46)
|
0.0001b
|
0-20
|
40 (5.69)
|
89 (9.09)
|
0.002
|
21-30
|
190 (27.03)
|
325 (33.20)
|
31-40
|
188 (26.74)
|
236 (24.11)
|
41-50
|
126 (17.92)
|
153 (15.63)
|
51-60
|
100 (14.22)
|
121 (12.36)
|
>60
|
59 (8.39)
|
55 (5.62)
|
Sex: Female/Male n, %
|
446 (58.99) / 310 (41.01)
|
590(56.57) / 453(43.43)
|
0.304
|
Vaccinated against influenza n, %
|
385 (50.93)
|
541 (51.87)
|
0.693
|
Comorbidities n, %
|
|
|
|
Overweight
|
150 (19.84)
|
181 (17.35)
|
0.179
|
Obesity
|
69 (9.13)
|
83 (7.96)
|
0.379
|
Hypertension
|
87 (11.51)
|
109 (10.45)
|
0.477
|
Diabetes
|
71 (9.39)
|
58 (5.56)
|
0.002
|
Immunodeficiency
|
8 (1.06)
|
10 (0.96)
|
0.834c
|
Number of comorbidities
|
4.489 ± 2.409
|
3.810 ± 2.423
|
0.008 d
|
Blood group n, %
|
|
|
|
A (Rh+ or RH-)
|
215 (28.44)
|
300 (28.76)
|
0.403
|
B (Rh+ or RH-)
|
61 (8.07)
|
94 (9.01)
|
AB (Rh+ or RH-)
|
19 (2.51)
|
32 (3.07)
|
O (Rh+ or RH-)
|
377 (49.87)
|
528 (50.62)
|
Unknown
|
84 (11.11)
|
89 (8.53)
|
Risk contact
|
|
|
|
Contact with COVID-19 patient n, %
|
508 (67.20)
|
768 (73.63)
|
0.003
|
Days of contact with COVID-19 patients pre-test Median (P25th-P75th)
|
12 (7-17)
|
10 (6-15)
|
0.0023 b
|
*Anti-SARS-CoV-2 IgM, IgG, or IgM+ IgG seropositivity; aChi-square, bKruskal-Wallis, c Fisher's exact test; d t-student. Bold text indicates a statistically significant difference with a p-value less than 0.05.
Symptoms of the study participants
The symptoms findings in seropositive cases and seronegative cases are shown in Table 2. Seropositive cases showed more days of symptom onset than seronegative cases (median 10 days [IQR: 7-14] vs. 8 days [IQR: 5-11], respectively, p<0.0001). Similarly, seropositive cases declared a greater number of symptoms than seronegative cases (median 5 symptoms [IQR: 3-6] vs. 4 symptoms [IQR: 2-6], respectively, p<0.0001).
The most prevalent symptom in both study groups was headache (67.20% in seropositive cases and 65.96% in seronegative cases, p = 0.585). On the other hand, hypogeusia, diarrhea, vomiting, upset stomach, pain chest, fatigue, and dizziness were the less frequent symptoms in both study groups (prevalency ≤6%). There were statistically significant differences in the frequency of cough, respiratory distress, muscle and joint pain, and anosmia between both study groups, all of which were most frequent in seropositive cases (p<0.0001).
Table 2. Symptoms of individuals negative or positive to anti-SARS-CoV-2 antibodies
Variables
|
Positive for anti-SARS-CoV-2 antibodies
|
Negative for anti-SARS-CoV-2 antibodies
|
P-value
|
N=756
|
N=1043
|
|
Days of symptom onset Median (P25th-P75th)
|
10 (7-14)
|
8 (5-11)
|
<0.0001
|
Number of symptoms Median (P25th-P75th)
|
5 (3-6)
|
4 (2-6)
|
<0.0001
|
Asymptomatic n, %
|
47 (6.22)
|
142 (13.61)
|
<0.0001
|
Headache n, %
|
508 (67.20)
|
688 (65.96)
|
0.585
|
Cough n, %
|
437 (57.80)
|
481 (46.12)
|
<0.0001
|
Fever n, %
|
246 (32.54)
|
307 (29.43)
|
0.159
|
Respiratory distressn, %
|
194 (25.66)
|
176 (16.87)
|
<0.0001
|
runny nose, nasal congestion, sneezing n, %
|
384 (50.79)
|
559 (53.60)
|
0.240
|
Muscle pain n, %
|
418 (55.29)
|
481 (46.12)
|
<0.0001
|
Joint pain n, %
|
285 (37.70)
|
306 (29.34)
|
<0.0001
|
Sore throat n, %
|
374 (49.47)
|
546 (52.35)
|
0.228
|
Anosmia n, %
|
453 (59.92)
|
305 (29.24 )
|
<0.0001
|
Hypogeusia n, %
|
39 (5.16)
|
27 (2.59)
|
0.004
|
Diarrhea, vomiting, upset stomach n, %
|
37 (4.89)
|
63 (6.04)
|
0.295
|
Chest pain n, %
|
5 (0.66)
|
12 (1.15)
|
0.290 c
|
Fatigue n, %
|
9 (1.19)
|
11 (1.05)
|
0.786 c
|
Dizziness n, %
|
5 (0.66)
|
12 (1.15)
|
0.290 c
|
*Anti-SARS-CoV-2 IgM, IgG, or IgM+ IgG seropositivity. Bold text indicates a statistically significant difference with a p-value less than 0.05
Symptoms according to seropositivity pattern to anti-SARS-CoV-2 antibodies
The frequency of symptoms reported among individuals with anti-SARS-CoV-2 IgM, IgG, or IgM+IgG seropositivity was similar (Table 3). However, those who presented IgM+IgG reported cough more frequently (61.6%) than those who only presented IgM (47.5%) (p = 0.007). Moreover, anosmia was more frequent in those who presented IgM+IgG (61.6%) than in those who presented IgG (49.6%) (p = 0.034).
Table 3. Symptoms according to seropositivity to anti-SARS-CoV-2 antibodies
Variables
|
Anti-SARS-CoV-2 IgM seropositivity
|
Anti-SARS-CoV-2 IgG seropositivity
|
Anti-SARS-CoV-2 IgM + IgG seropositivity
|
P-valuea
|
Days of symptom onset (Median, P25th-P75th)
|
N=69
|
N=66
|
N=270
|
|
9.00 (7.00-11.00)
|
10 (7.75-13.25)
|
10.00 (7.00-15.00)
|
0.086b
|
|
N=118
|
N=125
|
N=513
|
|
Number of symptoms (Median, P25th-P75th)
|
4.50 (3.00-6.00)
|
4.00 (2.00-6.00)
|
5.00 (3.00-6.50)
|
0.088b
|
Headache n, %
|
82 (69.5)
|
81 (64.8)
|
345 (67.3)
|
0.750
|
Cough n, %
|
56 (47.5)
|
65 (52.0)
|
316 (61.6)
|
0.007
|
Fever n, %
|
34 (28.8)
|
33 (26.4)
|
179 (34.9)
|
0.122
|
Respiratory distressn, %
|
24 (20.3)
|
23 (18.4)
|
147 (28.7)
|
0.022
|
Runny nose, nasal congestion, sneezing n, %
|
65 (55.1)
|
61 (48.8)
|
258 (50.3)
|
0.576
|
Muscle pain n, %
|
69 (58.5)
|
66 (52.8)
|
283 (55.2)
|
0.672
|
Joint pain n, %
|
48 (40.7)
|
40 (32.0)
|
197 (38.4)
|
0.324
|
Sore throat n, %
|
57 (48.3)
|
62 (49.6)
|
255 (49.7)
|
0.969
|
Anosmia n, %
|
75 (63.6)
|
62 (49.6)
|
316 (61.6)
|
0.034
|
Hypogeusia n, %
|
11 (9.3)
|
6 (4.8)
|
22 (4.3)
|
0.082
|
Diarrhea, vomiting, upset stomach n, %
|
7 (5.9)
|
2 (1.6)
|
28 (5.5)
|
0.174
|
Chest pain n, %
|
1 (0.8)
|
1 (0.8)
|
3 (0.6)
|
0.659c
|
Fatigue n, %
|
1 (0.8)
|
4 (3.2)
|
4 (0.8)
|
0.092c
|
Dizziness n, %
|
1 (0.8)
|
1 (0.8)
|
3 (0.6)
|
0.659c
|
aChi-square, bKruskal-Wallis, cFisher's exact test, Bold text indicates a statistically significant difference with a p-value less than 0.05.
Food intake quality
Three dietary patterns were identified by the cluster analysis (healthy, unhealthy, and habits in need of improvement). The healthy pattern was characterized by a higher intake of water, vegetables, fish, fruit, healthy fat, oilseeds/avocado, lean meat, legumes, and low intake of sweetened beverages, sweets or commercially produced desserts, processed foods, and alcohol. The unhealthy pattern group frequently consumed sweetened beverages, foods not prepared at home, sweets or commercially produced desserts, processed foods, alcohol, and infrequently consumed water, vegetables, fish, and fruit. The group with habits in need of improvement frequently consumed unhealthy fat and whole grains and rarely consumed oilseeds/avocado, foods not prepared at home, and legumes. The analysis of variance showed differences in these patterns (p<0.001) for each item of the questionnaire, and discriminant analysis confirmed that the dietary patterns had significant differences between them (p<0.001), as was expected.
The analysis of dietary patterns (Table 4) identified that only 34.4% of seropositive cases report healthy food intake. In contrast, seronegative individuals present this same pattern in 38.1% of the cases. However, this difference was not significant (p=0.221).
The individual food intake habits showed to be similar in both groups, except for the most consumed type of fat (p = 0.006), since 26.9% of the seronegative cases and 20% of seropositive cases consume monounsaturated fats more frequently than other types of fats. Conversely, 69% of the seronegative individuals and 74.7% of those seropositive cases consume polyunsaturated fats more frequently. In both groups, the optimal consumption of vegetables, fish, legumes, oilseeds, and avocado is infrequent (<15%).
Table 4. Food intake quality in individuals negative or positive to anti-SARS-CoV-2 antibodies
Question
|
Answer options
|
Positive for anti-SARS-CoV-2 antibodies*
N = 756
|
Negative for anti-SARS-CoV-2 antibodies
N = 1043
|
P-valuea
|
N (%)
|
N (%)
|
1. Do you drink at least 1.5 liters of water per day?
|
A. Never
|
16 (2.1)
|
23 (2.2)
|
0.141
|
B. Sometimes
|
237 (31.3)
|
285 (27.3)
|
C. Almost always
|
276 (36.5)
|
373 (35.8)
|
D. Always
|
227 (30.0)
|
362 (34.7)
|
2. Do you consume at least 200 grams of cooked or raw vegetables per day?
|
A. Never
|
17 (2.2)
|
35 (3.4)
|
0.104
|
B. Sometimes
|
376 (49.7)
|
466 (44.7)
|
C. Almost always
|
257 (34.0)
|
396 (38.0)
|
D. Always
|
106 (14.0)
|
146 (14.0)
|
3. Do you eat fresh or frozen fish (100 g) at least one day per week?
|
A. Never
|
122 (16.1)
|
146 (14.0)
|
0.351
|
B. Sometimes
|
452 (59.8)
|
641 (61.5)
|
C. Almost always
|
118 (15.6)
|
181 (17.4)
|
D. Always
|
64 (8.5)
|
75 (7.2)
|
4. Do you consume one or more glass (can) of sweetened beverages per week?
|
A. Never
|
116 (15.3)
|
193 (18.5)
|
0.319
|
B. 1 to 3 times
|
433 (57.3)
|
570 (54.7)
|
C. 4 to 6 times
|
114 (15.1)
|
162 (15.5)
|
D. Daily
|
93 (12.3)
|
118 (11.3)
|
5. Do you consume at least 200 grams of fruit per day?
|
A. Never
|
15 (2.0)
|
23 (2.2)
|
0.880
|
B. Sometimes
|
286 (37.8)
|
405 (38.8)
|
C. Almost always
|
294 (38.9)
|
408 (39.1)
|
D. Always
|
161 (21.3)
|
207 (19.1)
|
6. What type of fat do you consume most frequently on a weekly basis?
|
A. Monounsaturated
|
151 (20.0)
|
281 (26.9)
|
0.006
|
B. Polyunsaturated
|
565 (74.7)
|
720 (69.0)
|
C. Saturated
|
23 (3.0)
|
23 (2.2)
|
D. Do not know
|
17 (2.2)
|
19 (1.8)
|
7. Do you consume at least 30 grams of oilseeds or 1/2 of an avocado per day?
|
A. Never
|
54 (7.1)
|
61 (5.8)
|
0.351
|
B. Sometimes
|
423 (56.0)
|
566 (54.3)
|
C. Almost always
|
218 (28.8)
|
312 (29.9)
|
D. Always
|
61 (8.1)
|
104 (10.0)
|
8. Do you eat foods not prepared at home three or more days per week?
|
A. Never
|
71 (9.4)
|
118 (11.3)
|
0.576
|
B. Sometimes
|
465 (61.5)
|
624 (59.8)
|
C. Almost always
|
152 (20.1)
|
202 (19.4)
|
D. Always
|
68 (9.0)
|
99 (9.5)
|
9. What type of meat do you consume most often?
|
A. Red meat
|
399 (52.8)
|
516 (49.5)
|
0.361
|
B. Chicken
|
315 (41.7)
|
469 (45.0)
|
C. Fish
|
42 (5.6)
|
58 (5.6)
|
10. Do you eat processed foods two or more days per week?
|
A. Never
|
112 (14.8)
|
129 (12.4)
|
0.398
|
B. Sometimes
|
567 (75.0)
|
792 (75.9)
|
C. Almost always
|
70 (9.3)
|
112 (10.7)
|
D. Always
|
7 (0.9)
|
10 (1.0)
|
11. Do you consume sweets or commercially produced desserts two or more days per week?
|
A. Never
|
64 (8.5)
|
105 (10.1)
|
0.470
|
B. Sometimes
|
542 (71.7)
|
719 (68.9)
|
C. Almost always
|
120 (15.9)
|
182 (17.4)
|
D. Always
|
30 (4.0)
|
37 (3.5)
|
12. Do you eat legumes at least three days per week (300 g per week)?
|
A. Never
|
20 (2.6)
|
37 (3.5)
|
0.554
|
B. Sometimes
|
344 (45.5)
|
455 (43.6)
|
C. Almost always
|
295 (39.0)
|
426 (40.8)
|
D. Always
|
97 (12.8)
|
125 (12.9)
|
13. What type of cereals do you consume most often?
|
A. Whole grain
|
260 (34.4)
|
406 (38.9)
|
0.145
|
B. Minimally processed
|
256 (33.9)
|
329 (31.5)
|
C. Processed and ultra-processed
|
240 (31.7)
|
308 (29.5)
|
14. If you are a man, do you consume more than 2 alcoholic beverages per day? If you are a woman, do you consume more than 1 alcoholic beverage per day?
|
A. Never
|
519 (68.7)
|
716 (68.6)
|
0.077
|
B. Sometimes
|
228 (30.2)
|
296 (28.4)
|
C. Almost always
|
8 (1.1)
|
26 (2.5)
|
D. Always
|
1 (0.1)
|
5 (0.5)
|
Dietary patterns
|
Healthy food intake
|
260 (34.4)
|
397 (38.1)
|
0.221
|
Habits in need of improvement
|
357 (47.2)
|
453 (43.4)
|
Unhealthy food intake
|
139 (18.4)
|
193 (18.5)
|
*Anti-SARS-CoV-2 IgM, IgG, or IgM+ IgG seropositivity.
aChi-square. Bold text indicates a statistically significant difference with a p-value less than 0.05.