Epidemiological survey of elderly patients diagnosed with COVID-19 at mobile field hospitals

Abstract

BACKGROUND:

During the COVID-19 pandemic, the mobile field hospital, a rapidly deployable healthcare facility for emergency care, was effective in ensuring rapid diagnosis and treatment of patients with mild or asymptomatic SARS-CoV2 infections, effectively preventing the spread of COVID-19.

OBJECTIVE:

We conducted a survey to gain a thorough understanding of the epidemiological traits among the elderly who contracted the Omicron variant of the SARS-CoV-2 virus at a mobile field hospital set up at the National Exhibition and Convention Center (Shanghai).

METHODS:

A cross-sectional study approach was employed to examine various factors such as demographic characteristics, clinical features, vaccination status, and nucleic acid testing. We utilized the DezhenTech Integrated Electronic Medical Record Platform (Municipal Isolation Hospital) to collect data and focused on elderly individuals infected with COVID-19 in the fifth isolation zone of the mobile field hospital set up at the National Exhibition and Convention Center (Shanghai). The patients were categorized into different age groups for analysis.

RESULTS:

Among the 3,183 elderly patients, 54.7% were males and 45.3% were females, with an average age of 65.32 $\pm$ 4.41 years. Among them, 47.8% (1523/3183) were 60–64 years old, 34.0% (1082/3183) were 65–69 years old, 14.0% (444/3183) were 70–74 years old, 3.2% (103/3183) were 75–79 years old, and 1.0% (31/3183) were $\geqslant$ 80 years old. The majority (95.7%) of the elderly patients with chronic conditions had hypertension, diabetes, and coronary heart disease. The first viral nucleic acid screening showed a higher positive rate in the community and hospital fever clinics. The cumulative positive rate of the nucleic acid test in the mobile field hospital was 38.7%. The average CT value of the COVID-19 ORF1ab gene was 34.56 $\pm$ 5.98, while the average CT value of the N gene was 33.10 $\pm$ 6.50. The patients took an average of 3.40 $\pm$ 0.45 days to test negative, with a positive rate of 15.4% and an average hospital stay of 7.45 $\pm$ 0.53 days. The overall rate of COVID-19 vaccine coverage was 68.0%, with an enhanced coverage rate of 40% and a non-coverage rate of 29.3%.

CONCLUSIONS:

The overall prognosis for elderly patients who experienced a mild or asymptomatic SARS-CoV-2 Omicron infection at the mobile field hospital was favorable, although the vaccination rate in general was not high. By effectively managing underlying health conditions, the duration of their hospital stay in the mobile field hospital was reduced.

Keywords

Elderly patients epidemiology mobile field hospital SARS-CoV-2

1. Introduction

The persistent COVID-19 epidemic lasted more than two years and led to the SARS-CoV-2 virus undergoing several mutations, increasing the risk of severe illness and mortality among patients [1]. The spread of SARS-CoV-2 Omicron in Shanghai has been successfully contained. The mobile field hospital, a rapidly deployable healthcare facility for emergency care during the COVID-19 epidemic, was effective in ensuring rapid diagnosis and treatment of patients with mild or asymptomatic SAR-CoV2 infections, effectively preventing the spread of COVID-19. However, the elderly population, who make up a significant portion of the patients, emerged as a critical focus for prevention and treatment. Elderly patients present a complex situation due to the coexistence of multiple illnesses, aging, and weakened immune function. To gain a comprehensive understanding of the elderly patients with COVID-19, we conducted an epidemiological study of patients admitted to the fifth branch of the mobile field hospital set up at the National Exhibition and Convention Center (Shanghai).

2. Materials and methods

2.1 Participants

A cross-sectional study design was utilized to gather data on patients who met the criteria for COVID-19 infection [2] at the fifth branch of mobile field hospital set up at the National Exhibition and Convention Center (Shanghai). The data was collected between April 8 and May 31, 2022, using the DezhenTech Integrated Electronic Medical Record Platform (Municipal Isolation Hospital). We focused on elderly patients aged 60, stratified them by age, and reviewed their demographic and clinical characteristics, including gender, medical history, clinical manifestations, hospitalization, referrals, as well as COVID-19 vaccinations and nucleic acid test, stratified by age. These data are shown in Tables 1 and 2.

2.2 Sample collection

Patients admitted to the mobile field hospital were subjected to daily testing using a single-tube oral and pharyngeal swab. The daily testing was continued until two consecutive negative nucleic acid tests were obtained within a 24-hour period, following which, the patients underwent individual single tube testing of both oropharyngeal and nasopharyngeal swabs twice a week. Upon meeting the discharge criteria, patients underwent final testing, consisting of individual single and dual tube testing. When a patient had two consecutive nucleic acid tests with a CT value of $\geqslant$ 35 for both the N and ORF genes (fluorescent quantitative PCR method with a cutoff value of 40) and a sampling interval of at least 24 hours, all test samples were promptly transferred to the nucleic acid test institution using a centralized transfer box.

2.3 Nucleic acid test

The fluorescent reverse transcription-polymerase chain reaction (RT-PCR) technique was employed to identify the CT value (cycle threshold value) of the N gene and ORF1ab gene of the COVID-19 (SARS CoV-2) genetic material. The threshold set for detection was 40, and samples were collected at intervals of at least 24 hours. The testing kits were obtained from Wuhan EasyDiagnosis Biomedicine, and the amplification device used was the Molarry MA-6000. The testing process was conducted independently by Shanghai Labway Medical Laboratory.

Table 1
Demographic and clinical characteristics of elderly patients infected with COVID-19 Omicron variant [cases (%), mean $\pm$ SD]

Item	60–64 (years)		65–69 (years)		70–74 (years)		75–79 (years)		$\geqslant$ 80 (years)		Total		$t/\chi^{2}$	$P$ -value
	1523		1082		444		103		31		3183
Gender
Male	822	(54.0%)	596	(55.1%)	252	(56.8%)	58	(56.3%)	11	(35.5%)	1739	(54.7%)	5.87	0.209
Female	701	(46.0%)	486	(44.9%)	192	(43.2%)	45	(43.7%)	20	(64.5%)	1444	(45.3%)
History
Smoker	53	(3.5%)	34	(3.1%)	12	(2.7%)	3	(2.9%)	1	(3.2%)	103	(3.2%)	5.33	0.255
Hypertension	711	(46.7%)	533	(49.3%)	240	(54.1%)	50	(48.5%)	16	(51.6%)	1550	(48.7%)	7.81	0.099
Coronary heart disease	192	(12.6%)	139	(12.8%)	57	(12.8%)	13	(12.6%)	4	(12.9%)	405	(11.3%)	0.04	0.999
Arrhythmia	170	(11.2%)	125	(11.6%)	50	(11.3%)	12	(11.7%)	3	(9.7%)	360	(11.3%)	0.19	0.996
Diabetes	351	(23.0%)	250	(23.1%)	83	(18.7%)	22	(21.4%)	6	(19.4%)	712	(22.4%)	0.41	0.982
Malignant tumor	10	(0.6%)	12	(1.1%)	4	(0.9%)	2	(1.9%)	1	(3.2%)	29	(0.9%)	4.61	0.329
Clinical manifestations
Coughing	1130	(74.2%)	764	(70.6%)	317	(71.4%)	69	(67.0%)	25	(80.6%)	2305	(72.4%)	20.68	$<$ 0.01
Fatigue	963	(62.3%)	597	(55.2%)	301	(67.8%)	65	(63.1%)	24	(77.4%)	1950	(61.2%)	30.91	$<$ 0.01
Fever	437	(28.7%)	308	(28.5%)	120	(27.0%)	21	(20.4%)	5	(16.1%)	1572	(49.4%)	5.82	0.213
Muscle soreness	604	(39.7%)	445	(41.1%)	177	(39.9%)	44	(42.7%)	3	(9.7%)	1368	(42.9%)	12.85	$<$ 0.05
Reduced sense of taste	598	(39.3%)	436	(40.3%)	187	(42.1%)	40	(38.8%)	7	(22.6%)	1268	(39.8%)	5.16	0.271
Decreased appetite	471	(30.9%)	294	(27.2%)	127	(28.6%)	35	(33.9%)	11	(35.5%)	938	(29.5%)	6.01	0.198
Sore throat	423	(27.8%)	283	(26.2%)	128	(28.8%)	29	(28.2%)	9	(29.0%)	872	(27.4%)	1.47	0.830
Nasal congestion	373	(24.5%)	247	(24.0%)	105	(23.6%)	28	(27.2%)	8	(25.8%)	761	(23.9%)	1.66	0.797
Runny nose	282	(18.5%)	195	(18.0%)	78	(17.6%)	21	(20.4%)	6	(29.0%)	582	(18.3%)	0.59	0.965
Nausea	141	(9.3%)	110	(10.2%)	58	(13.0%)	13	(12.6%)	5	(16.2%)	327	(10.3%)	7.23	0.124
Diarrhea	92	(6.0%)	67	(6.2%)	34	(7.7%)	10	(9.7%)	3	(9.7%)	206	(6.5%)	3.95	0.413
Multi-organ failure	108	(7.1%)	76	(7.0%)	43	(9.7%)	12	(11.7%)	4	(12.9%)	243	(7.6%)	7.43	0.115
Number of transfers between designated hospitals	123	(8.4%)	90	(8.5%)	33	(8.6%)	14	(8.7%)	8	(8.8%)	268	(8.4%)	16.53	$<$ 0.05
Average length of stay	7.24 $\pm$ 0.48		7.32 $\pm$ 0.40		7.52 $\pm$ 0.42		7.35 $\pm$ 0.59		7.58 $\pm$ 0.52		7.45 $\pm$ 0.53		1.89	0.110

Table 2

Nucleic acid test and the vaccination of elderly patients infected with COVID-19 Omicron variant [cases (%), mean $\pm$ SD]

Item	60–64 (years)		65–69 (years)		70–74 (years)		75–79 (years)		$\geqslant$ 80 (years)		Total		$t/\chi^{2}$	$P$ -value
	1523		1082		444		103		31		3183
First screening positive pathway
Hospital fever clinic	406	(26.7%)	290	(26.8%)	119	(26.8%)	28	(27.2%)	9	(29.0%)	852	(26.7%)	0.10	0.998
Community nucleic acid test points	656	(43.0%)	465	(43.0%)	190	(42.8%)	45	(43.7%)	12	(38.7%)	1368	(43.0%)	0.26	0.992
Unit nucleic acid test point	214	(14.1%)	154	(14.2%)	63	(14.2%)	14	(13.6%)	5	(16.1%)	451	(14.2%)	0.14	0.997
Other nucleic acid test points	247	(16.2%)	173	(16.0%)	72	(16.2%)	16	(15.5%)	5	(16.1%)	512	(16.1%)	0.05	0.999
COVID-19 nucleic acid test
Cumulative times of nucleic acid test	7936	(5.2)	5644	(5.2)	2306	(5.2)	530	(5.1)	188	(6.0)	16604	(5.2)	0.91	0.923
Cumulative number of positive nucleic acid tests	3005	(2.0)	2100	(1.9)	950	(2.1)	245	(2.40)	120	(3.9)	6420	(2.0)	0.66	0.83
ORF1ab gene CT value	36.50 $\pm$ 5.07		34.69 $\pm$ 6.46		33.12 $\pm$ 5.32		32.12 $\pm$ 5.64		32.40 $\pm$ 5.42		34.56 $\pm$ 5.98		24.44	$<$ 0.01
N gene CT value	36.88 $\pm$ 3.92		34.27 $\pm$ 5.75		33.13 $\pm$ 5.57		30.97 $\pm$ 4.59		30.77 $\pm$ 5.24		33.10 $\pm$ 6.50		22.99	$<$ 0.01
Period (in days) when nucleic acid results first	3.37 $\pm$ 0.44		3.61 $\pm$ 0.32		3.56 $\pm$ 0.45		3.48 $\pm$ 0.51		3.23 $\pm$ 0.41		3.40 $\pm$ 0.45		2.43	0.464
become negative for COVID-19
Number of cases of COVID-19 nucleic acid	226	(14.8%)	160	(14.8%)	80	(18.0%)	17	(16.5%)	8	(25.8%)	491	(15.4%)	5.68	0.224
re-positivity
COVID-19 vaccination
Not vaccinated	443	(29.0%)	301	(27.8%)	135	(30.4%)	34	(33.0%)	20	(64.5%)	933	(29.3%)	20.68	$<$ 0.01
Vaccinated 1 dose	39	(2.6%)	28	(2.6%)	12	(2.7%)	4	(3.9%)	3	(9.7%)	86	(2.7%)	6.45	0.168
Vaccinated 2 doses	437	(28.7%)	308	(28.5%)	120	(27.0%)	21	(20.4%)	5	(16.1%)	891	(28.0%)	5.82	0.213
Vaccinated 3 doses	604	(39.7%)	445	(41.1%)	177	(39.9%)	44	(42.7%)	3	(9.7%)	1273	(40.0%)	12.85	$<$ 0.05
COVID-19 vaccination category
SINOVAC LIFE SCIENCES	754	(49.5%)	558	(51.6%)	220	(49.5%)	49	(47.6%)	8	(25.8%)	1589	(49.9%)	8.75	0.068
CNBJ	243	(10.8%)	162	(14.9%)	64	(14.4%)	15	(14.5%)	2	(6.5%)	486	(15.3%)	2.78	0.595
WHBIO	43	(1.9%)	31	(2.9%)	13	(3.0%)	3	(2.9%)	1	(3.2%)	91	(2.9%)	0.03	0.999
CanSino Bio	24	(1.0%)	18	(1.7%)	7	(1.6%)	1	(1.0%)	0	(0.0%)	50	(1.6%)	0.79	0.939
Zhifei longcom biopharmaceutical	16	(0.7%)	12	(1.1%)	5	(1.1%)	1	(1.0%)	0	(0.0%)	34	(1.0%)	0.38	0.984

2.4 Statistical methods

We employed PEM3.1 Medical Statistics Software for data analysis. For measurement data with a normal distribution, the results are presented as mean $\pm$ standard deviation. To compare groups, the two independent samples $t$ -test was utilized. Counting data are expressed as percentages, and Scheffé’s method was employed for making multiple comparisons of rates. Intragroup comparisons were carried out using the chi-squared test, and all tests were conducted using a bilateral approach. A statistically significant difference was considered when the $p$ -value was less than 0.05 ( $p<$ 0.05).

3. Results

3.1 Demographic characteristics

A total of 24,666 patients who fulfilled the criteria for discharge were included in the study. Among these patients, 3,183 were elderly individuals. Out of the elderly patients, 1,739 were males, accounting for 54.63% of the total (1739/3183), and 1,444 were females, accounting for 45.36% (1444/3183). The highest age recorded for females was 87, while for males, it was 82. The average age of the patients was 65.32 $\pm$ 4.41. When examining the age distribution, there were 1,523 cases aged 60–64, 1,082 cases aged 65–69, 444 cases aged 70–74, and 134 cases aged over 75. The respective proportions were 47.8% (1523/3183), 34.0% (1082/3183), 14.0% (444/3183), and 4.2% (134/3183). However, the differences in the distribution of male and female patients among the various age groups were not statistically significant ( $\chi^{2}=$ 5.87, $P=$ 0.209).

3.2 Clinical characteristics

A total of 104 patients (3.4%, 104/3,183 cases) were smokers. Among the elderly patients, 95.7% (3,047/3,183 cases) had pre-existing chronic conditions, including 48.7% (1,550/3,183 cases) with hypertension, 23.0% (732/3,183 cases) with diabetes, 12.7% (405/3,183 cases) with coronary heart disease, 11.3% (360/3,183 cases) with arrhythmia, and over 70% with cardiovascular diseases, with diabetes being the most common. The initial signs of the disease primarily included coughing (72.4%, 2,305/3,183 cases), fatigue (61.2%, 1,950/3,183 cases), fever (49.4%, 1,572/3,183 cases), followed by muscle soreness (42.9%, 1,368/3,183 cases), reduced sense of taste (39.7%, 1,268/3,183 cases), decreased appetite (29.5%, 938/3,183 cases), as well as sore throat (27.4%, 872/3,183 cases), nasal congestion (34.9%, 761/3,183 cases), runny nose (18.3%, 582/3,183 cases), nausea (10.3%, 327/3,183 cases), and flu-like symptoms such as diarrhea (6.5%, 206/3,183 cases). The number of cases with coughing, fatigue, and muscle soreness were significantly different among all age groups. The elderly COVID-19 patients stayed in the mobile field hospital for a duration ranging from 2 to 25 days, with an average stay of 7.45 $\pm$ 0.53 days. Among them, 268 patients were transferred to specialized hospitals for intensive treatment due to worsening of their underlying chronic conditions. There was a significant difference in the comparison of multi-sample rates ( $\chi^{2}=$ 16.54, $P=$ 0.002).

3.3 Nucleic acid test and the vaccination

The initial viral nucleic acid screening yielded the following results: in the community (residential areas where health service organizations are permanently stationed), the positive rate was 43.0% (1,368/3,183); in fever clinics in hospitals above the second level, it was 26.7% (852/3,183); at other nucleic acid test points (free testing sites jointly established by local CDC departments and hospitals at all levels), it was 16.1% (512/3,183); and at unit nucleic acid test points (internal testing sites established by administrative, institutional and business units for the purpose of prevention and control of the epidemic), it was 14.2% (451/3,183). The average number of days since the first visit to a testing center was 4.13 $\pm$ 0.27 days. The above data were provided by the local CDC department and entered into the DezhenTech Integrated Electronic Medical Record Platform by the medical staff when the patients were admitted to the mobile cabin hospital.

In the mobile field hospital, the cumulative positive rate of nucleic acid tests was 38.7% (6,420/16,604), with an average of 5.2 tests conducted per person. The average CT value for the ORF1ab gene of COVID-19 was 34.56 $\pm$ 5.98, and for the N gene, it was 33.10 $\pm$ 6.50. The average number of days for the nucleic acid to become negative was 3.40 $\pm$ 0.45 days, and the rate of re-positivity was 15.4% (491/3,183).

The coverage rate of COVID-19 vaccines was 68.1% (2,168/3,183), with an enhanced coverage rate of 40% (1,273/3,183) and a non-coverage rate of 29.3% (933/3,183). Among non-vaccinated patients, a comparison of multiple sample rates revealed significant differences ( $\chi^{2}=$ 20.68, $P=$ 0.0004). Regarding vaccination, the coverage rate of the COVID-19 inactivated vaccine was 96.2% (2,166/2,250), the adenovirus viral vector vaccine had a coverage rate of 2.3% (50/2,250), and the recombinant subunit vaccine had a coverage rate of 1.5% (34/2,250).

4. Discussion

New variants of the SARS-CoV-2 Omicron have been detected in 57 countries worldwide since the first mutation occurred on November 24, 2021. Research indicates that this new Omicron variant is more contagious and significantly more elusive compared to the early COVID-19 strain. It can evade the partial immune protection provided by prior infection and vaccination [3, 4, 5]. Consequently, during the initial stages of the COVID-19 outbreak in Shanghai, there was a rapid increase in the number of infected individuals due to the covert nature and swift spread of the disease. Nevertheless, the mobile field hospitals played a crucial role by promptly admitting many infected individuals, effectively containing the spread of the disease. Their effectiveness in epidemic prevention and control has been successfully demonstrated in Wuhan [6]. The Omicron variant of the SARS-CoV-2 virus can cause pneumonia, severe acute respiratory syndrome, kidney failure, and even death [7]. The severity of these consequences is linked to a combination of factors such as gender, age, pre-existing health conditions, and genetic factors, which interact with the virus and the genetic makeup of the host. Furthermore, genetic variations in SARS-CoV-2 are associated with certain genes involved in the host’s immune response, including angiotensin converting enzyme 2, transmembrane serine protease 2, interferon, interleukin, toll-like receptor, and others [8, 9].

Specifically, during the Shanghai epidemic, the average age of the dead due to COVID-19 was 80.4 years old, and all deaths were attributed to underlying diseases or the worsening of existing tumors. Among the elderly patients admitted to the mobile field hospital during the same period, comprising 12.9% (3,183/24,666) of all patients, most were between the ages of 60 and 75, with no significant gender difference. More than 50% of the elderly patients had at least two pre-existing health conditions, primarily related to the cardiovascular system. Hypertension accounted for 48.7%, diabetes for 23.0%, coronary heart disease for 12.7%, while conditions such as tumors, thrombosis, and lung diseases were less common. Common initial symptoms among elderly patients included cough, fatigue, and fever, while non-respiratory symptoms like loss of taste, muscle soreness, poor appetite, nausea, and diarrhea were also frequently observed. These findings align with previous studies conducted in China [10].

However, the elderly patients in the mobile field hospital mainly experienced mild or asymptomatic cases of COVID-19. To treat these patients, a combination of traditional Chinese medicine, including Lianhua Qingwen, Jingyin Gubiao Formula, Huashi Baidu Keli, Huoxiang Zhengqi Soft Jiaonang, and other drugs, was used based on the clinical symptoms and differentiation of the patients. This treatment plan resulted in significant relief or partial improvement of many symptoms. Preventing coronavirus disease requires two main approaches: implementing measures to reduce its transmission and ensuring effective vaccination. Vaccination has been proven to significantly decrease severe illness and mortality related to the disease [11]. In Hong Kong, during the fifth wave of the COVID-19 epidemic, individuals over 60 years old who were not vaccinated had a mortality rate that was nine times higher compared to those who had received the vaccine. Consequently, the global immunization strategy has prioritized vaccinating the elderly and individuals with chronic underlying diseases. According to the results of our survey in the mobile field hospital, the overall COVID-19 vaccine coverage rate for elderly patients was 68.0%, with an enhanced coverage rate of 40%. These figures are close to the overall coverage rate of 62% and the enhanced coverage rate of 38% for elderly patients aged 60 years and above, as reported by the Shanghai Municipal Health Commission [12, 13]. The variation in vaccine coverage may be attributed to the presence of underlying diseases and the level of awareness regarding viral infections among some patients during the vaccination process. The nucleic acid CT value represents the number of cycles needed for the fluorescence signal in each reaction tube to reach a predetermined threshold. A higher concentration of viral nucleic acid leads to increased fluorescence intensity and a lower cycle threshold CT. The results of this survey on the flow of patients revealed that elderly patients who were discharged from the mobile field hospital had the lowest CT values for the ORF1ab gene and N gene, which were 19.78 and 18.07, respectively. On average, the CT values were 34.56 $\pm$ 5.98 and 33.10 $\pm$ 6.50 for the two genes. These findings suggest that the concentration of viral nucleic acid in elderly patients with COVID-19 infection approached the level of recovery after receiving appropriate treatment. However, 15.4% of elderly patients still showed a positive reaction, leading to longer hospital stays compared to other patients during the same period. The maximum duration of hospitalization was 25 days. It should be noted that the CT value of the nucleic acid test was influenced by various factors, including the sample, testing conditions, and testing equipment. Even if the same sample was tested multiple times, the CT value may not be entirely consistent.

This study is limited by its sample selection, which was confined to patients from the mobile field hospital of the National Exhibition and Convention Center (Shanghai), without considering cases from other institutions in Shanghai. Consequently, the generalizability of the findings is constrained. Additionally, the possible reason for short-term re-positivity in the COVID-19 nucleic acid test among certain elderly patients and its potential long-term impact on vital organ function, as well as the psychological distress, have not been thoroughly investigated. Further investigations involving broader case inclusion and a long-term follow-up are warranted.

5. Conclusion

The overall prognosis of the elderly patients with COVID-19 infection who were admitted to the mobile field hospital was good, and effective control of basic diseases and passive immunity could have shortened their hospital stay.

Footnotes

Conflict of interest

None to report.

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Epidemiological survey of elderly patients diagnosed with COVID-19 at mobile field hospitals

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Materials and methods

2.1 Participants

2.2 Sample collection

2.3 Nucleic acid test

Table 1 Demographic and clinical characteristics of elderly patients infected with COVID-19 Omicron variant [cases (%), mean ± SD]

3. Results

3.1 Demographic characteristics

3.2 Clinical characteristics

3.3 Nucleic acid test and the vaccination

4. Discussion

5. Conclusion

Footnotes

Conflict of interest

References

Table 1
Demographic and clinical characteristics of elderly patients infected with COVID-19 Omicron variant [cases (%), mean $\pm$ SD]