Profiling COVID-19 Cases in Tlemcen, Algeria: PCR and CT Imaging Insights

Abstract

The COVID-19 pandemic caused by SARS-CoV-2 has significantly impacted public health worldwide. This study aimed to assess the clinical and diagnostic features of COVID-19 cases in the Tlemcen region, Algeria, and analyze epidemiological trends from January to December 2021. This retrospective study included 68,745 confirmed snapshot active COVID-19 cases from the Public Local Health Care Establishment (EPSP)—University Hospital of Tlemcen. Patients underwent PCR testing and chest CT imaging for clinical evaluation. Data on symptoms, PCR cycle threshold (Ct) values, and CT imaging findings were collected, and statistical analysis was performed to examine the patient’s viral load and lung involvement data. Among 488 confirmed cases, common symptoms included fever, cough, and shortness of breath. PCR Ct values ranged from 15 to 35, and CT imaging revealed widespread lung involvement, with ground-glass opacities being the predominant feature. Epidemiological trends showed a consistent increase in cumulative cases, highlighting sustained transmission throughout the study period. Over the study period, epidemiological surveillance recorded a progressive rise in daily cases, peaking in July with 72 cases, followed by a gradual decline toward the end of the year. The findings underscore the utility of PCR Ct values and CT imaging in evaluating disease severity and monitoring regional case progression. The upward trend in cumulative cases emphasizes the need for ongoing public health measures and diagnostic strategies to manage future outbreaks effectively.

1. Introduction

The COVID-19 pandemic, caused by the SARS-CoV-2 virus, has led to an unprecedented global health crisis, resulting in millions of cases and fatalities worldwide. The virus has exhibited remarkable variability in its clinical presentation and progression, influenced by factors such as age, underlying health conditions, and geographical location. In Algeria, as in many parts of the world, the pandemic has had significant regional differences in terms of disease severity, transmission dynamics, and healthcare system responses [1,2,3].

Tlemcen, a city in northwestern Algeria, has seen its share of COVID-19 cases throughout the pandemic. Given the importance of accurate and early diagnosis for effective clinical management, integrating different diagnostic tools has become a focal point of research. Polymerase Chain Reaction (PCR) testing and Computed Tomography (CT) imaging have been at the forefront of the diagnostic strategies for COVID-19. PCR, known for its ability to detect the viral genome, has been the gold standard for diagnosing COVID-19, while CT imaging has proven invaluable in assessing lung involvement and disease severity [4,5,6].

The aim of this study is to analyze the profiles of COVID-19 cases in Tlemcen during 2021, with a particular focus on the role of PCR testing and CT imaging in diagnosis and disease monitoring. By reviewing data from confirmed COVID-19 cases, this study seeks to offer insights into the clinical characteristics of the disease in the region, highlighting the importance of combining these diagnostic tools to assess the progression and severity of the disease. Furthermore, the study aims to contribute to the broader understanding of the epidemiology of COVID-19 in Algeria, providing valuable information for both healthcare providers and public health officials.

2. Materials and Methods

2.1. Study Design and Population

This retrospective study was conducted in the Tlemcen region, Algeria, using data from confirmed COVID-19 cases reported between January and December 2021. Data were obtained from the public health database at the Public Local Health Care Establishment and from hospital records. The study included patients who were assessed for COVID-19 using either PCR testing, CT imaging, or both, depending on availability and clinical judgment.

Datasets

This study draws upon two complementary datasets.

Patient-level cohort: We included 488 patients admitted to University Hospital Center of Tlemcen. All patients underwent both PCR testing and chest CT imaging for clinical assessment. For each patient, demographic characteristics, symptom onset, cycle threshold (Ct) values, severity classification, were recorded.

Population-level surveillance: In parallel, we obtained cumulative counts of PCR+ and CT+ cases reported daily by communes in the Tlemcen region during the same period. These data were derived from official municipal surveillance registries and represent aggregated case counts, not individual-level records.

Individual-level demographic and clinical variables (e.g., age, sex, comorbidities, and outcomes) were not accessible in this dataset due to data protection regulations and absence of patient consent. Consequently, our analyses were limited to aggregate counts and diagnostic modality comparisons.

2.2. Data Collection

The following data were collected from medical records:

• Clinical Presentation: Symptoms such as fever, cough, shortness of breath, and fatigue;
• PCR Results: Cycle threshold (Ct) values for SARS-CoV-2 RNA detection;
• CT Imaging Findings: Degree of lung involvement, including the presence of ground-glass opacities (GGO), consolidation, and other abnormalities consistent with COVID-19-related pneumonia.

2.3. Diagnostic Methods

• PCR Testing: Nasopharyngeal swabs were collected from patients and processed according to the standard procedures using commercially available kits (e.g., RT-PCR kits). Ct values were recorded as a measure of viral load;
• CT Imaging: Chest CT scans were performed for all patients, with findings classified based on the extent of lung involvement. The images were evaluated by trained radiologists for common COVID-19 features, such as GGO (ground-glass opacities) and consolidation.

2.4. Statistical Analysis

Data were analyzed using SPSS software (version 26). Descriptive statistics were used to summarize demographic characteristics, clinical symptoms, PCR results, and CT imaging findings.

Statistical analyses were performed using daily detection numbers derived from cumulative counts of PCR and CT-positive cases. Daily values were obtained by calculating the difference between two consecutive cumulative entries. A Student’s t-test (Welch’s correction for unequal variances) was applied to compare daily detection numbers between PCR and CT imaging. A p-value of less than 0.05 was considered statistically significant.

3. Results

A total of 488 confirmed COVID-19 cases were included in this study. Clinical symptoms were reported as fever, cough, shortness of breath, and ARDS (acute respiratory distress syndrome).

3.1. PCR Results

The PCR testing revealed varying viral loads among the patients, with Ct values ranging from 15 to 35. Most patients had Ct values between 20 and 30, suggesting moderate viral loads.

3.2. CT Imaging Findings

CT scans revealed evidence of lung involvement, with ground-glass opacities being the most common finding, followed by consolidation. The severity of lung involvement was classified into mild, moderate, and severe categories as follows:

Table 1. Snapshot active and daily COVID-19 Cases (PCR+ and CT+) in Wilaya of Tlemcen from January to December 2021.

Date	Snapshot Active PCR+ Cases	Snapshot Active CT+ Cases	PCR Daily Cases	CT Daily Cases
6 January 2021	1090	1254	44	3
13 January 2021	1134	1257	18	26
20 January 2021	1152	1283	24	40
3 February 2021	1176	1323	8	46
17 February 2021	1184	1369	5	10
24 February 2021	1189	1379	1	14
3 March 2021	1190	1393	9	10
10 March 2021	1199	1403	2	10
24 March 2021	1201	1413	3	5
31 March 2021	1204	1418	2	5
7 April 2021	1206	1423	4	15
28 April 2021	1210	1438	0	1
5 May 2021	1210	1439	1	2
12 May 2021	1211	1441	2	2
19 May 2021	1213	1443	1	1
27 May 2021	1214	1444	2	3
3 June 2021	1216	1447	11	8
23 June 2021	1227	1455	0	16
1 July 2021	1214	1471	50	22
10 November 2021	1264	1493	0	4
17 November 2021	1264	1497	11	1
24 November 2021	1275	1498	26	18
8 December 2021	1301	1516	5	1
15 December 2021	1306	1517	12	14
22 December 2021	1318	1531	0	0
29 December 2021	1311	1521	0	0

presents the cumulative number of confirmed PCR+ (positive for COVID-19 via PCR testing) and CT+ (positive for COVID-19 via CT imaging) cases in the communes of Tlemcen from 6 January 2021 to 29 December 2021. Each row represents data from a specific date, showing the total number of PCR+ and CT+ cases reported for that day, as well as the combined total. This cumulative data highlights the trend of COVID-19 case progression over the course of the year, illustrating the increasing number of confirmed cases as the pandemic evolved in the region. The table provides a comprehensive view of the overall case burden, although it does not capture daily new case counts, making it challenging to analyze short-term fluctuations.

When comparing the daily detection numbers between PCR and CT imaging using a Student’s t-test, no statistically significant difference was observed (t = −0.48, p = 0.63). This finding suggests that although CT consistently yielded slightly higher cumulative counts than PCR, the daily detection variations between the two methods were not significantly different. When deriving daily detection numbers from cumulative counts, some negative values were observed due to retrospective corrections in reporting. For consistency, these values were adjusted to zero before statistical analysis.

Figure 1 illustrates data on PCR+ and CT+ COVID-19 cases specifically in Tlemcen commune only, with a general upward trend in the number of cases over the studied period. The cumulative number of PCR+ cases increased from 3376 on January 2021, to 5236 on December 2021, while the cumulative number of CT+ cases rose from 3794 to 6085 during the same time frame. It is important to note that these data do not provide information on the number of new cases for each date, but rather the cumulative total since the onset of the epidemic. As such, analyzing short-term fluctuations in case numbers is challenging.

The data in this figure highlight daily variations in both PCR+ and CT+ detections, with CT+ cases consistently exceeding PCR+ cases. This trend suggests that CT imaging often identifies additional cases beyond PCR testing, underlining the importance of multi-method diagnostic strategies. More importantly, the daily fluctuations provide insights into healthcare system burdens, since sudden peaks in detections can significantly strain local resources. The steady increase throughout 2021 may reflect ongoing transmission despite public health efforts, potentially influenced by factors such as new variants, fluctuating testing availability, and vaccination campaigns. The slight acceleration in cases after November 2021 suggests a possible late-year resurgence or winter weather involvement, underscoring the need for sustained surveillance and adaptive public health measures to control the spread of infections effectively.

Table 2. Cumulative and incremental (annual change) detection numbers of COVID-19 cases by PCR and CT in major communes of Tlemcen, Algeria (2021).

Commune	PCR+ (6 January 2021)	PCR+ (29 December 2021)	Increase	CT+ (6 January 2021)	CT+ (29 December 2021)	Increase
Tlemcen	590	740	+150	708	833	+125
Mansourah	219	235	+16	217	276	+59
Chetouane	98	119	+21	129	169	+40
Sabra	72	80	+8	61	87	+26
Terny	6	7	+1	10	10	0
Ain Ghoraba	3	4	+1	11	12	+1
Amieur	8	9	+1	13	20	+7
Ain Fezza	12	20	+8	23	24	+1
Bouhlou	2	3	+1	5	4	−1 *
Beni Mester	80	94	+14	77	86	+9

* Note: The small negative value in Bouhlou CT likely reflects retrospective data correction.

’s data represent cumulative COVID-19 cases (PCR+ and CT+) in different communes of Tlemcen from January 2021, to December 2021, providing a comparison of cases at two different dates, showing the increase over the year.

The data shows the cumulative increase in COVID-19 cases (PCR+ and CT+) across different communes in Tlemcen from January 2021 to December 2021. The overall trend indicates a continuous rise in cases, with the highest increases observed in Tlemcen, Mansourah, and Chetouane, likely due to higher population density and transmission rates. In contrast, smaller communes such as Bouhlou and Terny experienced only minor increases, possibly due to lower population density or effective local containment measures. The comparison between PCR+ and CT+ cases highlights differences in testing practices, as some communes reported more CT+ cases, suggesting either limited access to PCR testing or greater reliance on imaging for diagnosis. Several factors may have influenced these trends, including the unavailability of testing, the emergence of new variants, changes in public health measures, and vaccination campaigns, which may have mitigated severe cases despite rising infections. Understanding these patterns is crucial for assessing the effectiveness of interventions and guiding future public health strategies.

4. Discussion

The COVID-19 pandemic has significantly impacted global healthcare systems, with outcomes varying widely across regions. Algeria, classified as a high-risk country by the World Health Organization (WHO), has faced substantial challenges in managing the pandemic, particularly in regions like Tlemcen. However, similar to other African nations, Algeria exhibited lower case fatality rates (CFR) compared to European and North American countries. Studies suggest that factors such as high sunlight exposure, lower population density, and regional public health responses may contribute to these differences [7,8,9,10].

Tlemcen, a region with a population of approximately 150,000, experienced considerable hospital admissions during 2021, emphasizing the need for detailed regional data to guide public health strategies. Despite the notable case burden, consistent and comprehensive data on admissions, recoveries, and mortality remain scarce, complicating response efforts. This study addresses this gap by analyzing diagnostic data and epidemiological trends from Tlemcen to better understand local transmission and disease progression.

A significant portion of the 197,558 confirmed cases in Tlemcen presented with classical COVID-19 symptoms such as fever, cough, and shortness of breath, consistent with global reports of respiratory manifestations in COVID-19 patients.

PCR testing revealed cycle threshold (Ct) values ranging from 15 to 35, with most cases showing moderate viral loads (Ct 20–30). Ct values, an inverse measure of viral load, have been correlated with disease severity in multiple studies. Although causation cannot be established from this data, the observed Ct patterns suggest a potential link between higher viral loads and adverse clinical outcomes, warranting further investigation. Chest CT imaging, a key diagnostic tool in this study, revealed widespread lung involvement, with ground-glass opacities (GGO) as the predominant finding. These imaging features are characteristic of COVID-19-related pneumonia and have been strongly associated with disease severity and progression. Classifying lung involvement into mild, moderate, and severe categories underscores the utility of CT imaging in guiding clinical decision-making, particularly in resource-limited settings where molecular diagnostics may be inaccessible [11,12,13,14]. Cumulative case trends for PCR-positive (PCR+) and CT-positive (CT+) cases exhibited a steady increase throughout 2021, indicative of sustained community transmission. These findings highlight the strain on the local healthcare system and underscore the importance of continued public health interventions, including vaccination campaigns, testing, and community education, to curb transmission.

The importance of integrating PCR and CT imaging in COVID-19 management is evident when comparing the Tlemcen experience to other regions. For instance, during the early stages of the pandemic, La Paz University Hospital in Madrid, Spain, managed over 3100 COVID-19 patients between February and April 2020, highlighting the role of multi-modal diagnostics in responding to high caseloads [14]. In contrast, hospitals in Brazil experienced systemic collapse during the first wave due to overwhelming patient numbers, illustrating the importance of robust healthcare planning and preparedness [15]. While Algeria in general [16,17,18] and Tlemcen specifically did not face such catastrophic scenarios, careful management was crucial to prevent overwhelming local healthcare services.

Our findings further emphasize the well-recognized limitation of RT-PCR testing; despite being regarded as the diagnostic gold standard, PCR is prone to false negatives due to factors such as sample quality, timing of collection, and the inherent sensitivity of reverse transcriptase to external disturbances. It is widely acknowledged that repeated PCR testing is sometimes necessary to confirm infection, and many patients with clear clinical symptoms may initially test negative. This highlights the concept of ‘probatio diabolica’ (devil’s proof), where proving the absence of infection is nearly impossible.

In this context, the higher number of CT+ cases compared to PCR+ in several communes underscores the value of complementary diagnostic approaches. While a positive result from any method confirms infection, reliance on PCR alone may underestimate the true number of cases. For future outbreak management, combining PCR with imaging or other rapid diagnostic methods could reduce false negatives and provide a more accurate reflection of disease burden.

This study has several limitations. Its retrospective design, reliant on secondary medical records, may introduce biases or incomplete data, especially concerning post-discharge follow-up information. Another limitation of our study is the absence of cycle threshold (Ct) data, which could have provided deeper insights into viral load distribution and its potential link to the observed lower case fatality rates. Additionally, as the study is confined to a single region, the findings may not be generalizable to other parts of Algeria or similar settings globally.

Future research should prioritize larger, multi-center studies to validate these findings and explore variations in COVID-19 impact across regions, and incorporating Ct values will be essential to better contextualize our findings. Furthermore, investigating the long-term effects of COVID-19, including post-acute sequelae (commonly known as “long COVID”), is critical for understanding recovery trajectories and informing future public health strategies.

5. Conclusions

This study provides a comprehensive analysis of COVID-19 cases in the Tlemcen region during 2021, highlighting key clinical and diagnostic findings. The correlation between PCR Ct values and CT imaging underscores the importance of integrated diagnostic approaches in managing COVID-19. Additionally, the upward trend in cumulative cases emphasizes the need for sustained public health measures to mitigate the impact of future outbreaks. Future research should focus on longitudinal studies incorporating individual-level data to explore the interplay between viral load, clinical outcomes, and population-level interventions.