SARS-CoV-2 test positivity among case finding strategies in Zambia, April-August 2020

Dabwitso Jezreel Banda^1,2,&, Warren Malambo³, Jonas Zajac Hines³, Ernest Kateule^{1, 2}, Muzala Kapina¹, Nyambe Sinyange^{1, 2}

 

¹Zambia National Public Health Institute, Lusaka, Zambia, ²Zambia Field Epidemiology Training Program, Lusaka, Zambia, ³U.S Centers for Disease Control and Prevention, Lusaka, Zambia

 

 

^&Corresponding author
Dabwitso Jezreel Banda, Zambia National Public Health Institute, 13 Reedbuck Road, Kabulonga, P. O. Box 30205, Lusaka-Zambia. bandadb3@gmail.com

 

 

 

 

Following the declaration of a SARS-CoV-2 outbreak in Zambia in March 2020, surveillance was heightened at community, health facility, district, provincial and national levels. Surveillance activities in Zambia included screening of travellers entering the nation at points of entry, contact tracing of persons with positive SARS-CoV-2 results, alerts of possible SARS-CoV-2 among persons from community who are experiencing symptoms of SARS-CoV-2, health facility testing and special operations. Special operations wherein a group of public health workers are mobilized to test a large number of persons who share a potential exposure (e.g, a cluster identified in workplace) was done in certain hotspots within Lusaka, Central and Muchinga provinces to ascertain the extent of the outbreak and prevent the spread of SARS-CoV-2 [1-4].

 

The number patients with SARS-CoV-2 increased more rapidly from July, 2020. Zambia recorded 17,243 confirmed cases of SARS-CoV-2, 353 deaths, and 16,473 recoveries as of 17 November, 2020. Testing positivity is an important indicator of disease transmission as well as testing modality efficiency. With rapid increase in cases, testing demand is expected to increase. In order to meet this demand, efficient testing strategies should be prioritized over inefficient ones due to limited testing capacity. To date, no data have been published describing the positivity rates for different case finding strategies for SARS-CoV-2 in Zambia.

 

The aim of this study was to assess the SARS-CoV-2 positivity among contacts, alerts (call center and health facilities), special operations and points of entry testing and to establish factors associated with positive SARS-CoV-2 cases among them.

 

 

We conducted a cross-sectional study of all persons tested for SARS-CoV-2 in Zambia from 1 April to 13 August 2020. The study population was persons who had undergone SARS-CoV-2 testing in Zambia from April to August 2020 and entered into a SARS-CoV-2 polymerase chain reaction (PCR) test results database maintained by the Zambia National Public Health Institute. Only individuals with lab results and information on case finding strategy used to identify them for testing were included in our analysis. All persons consented to testing during their care for COVID-19. All data used in this study were de-identified. The analysis included test results from 7,352 health facility alerts, 725 community alerts, 6,196 contacts, 1,790 points of entry and 11,384 special operations individuals.

 

Data were extracted from the data base and assessed for completeness. Records with missing SARS-CoV-2 results and case find strategy were removed from the analysis. Variables that were extracted included date when sample was collected, screening point, province, district, sub district, age, sex, case finding strategy, history of contact to a SARS-CoV-2 patient and lab results. Persons with multiple tests were not double counted.

 

Case finding strategies were classified as: contact tracing, community alerts, health facility testing, special operations and points of entry. Age was categorized into 10-years age bands. The positivity rate was defined as the number of persons who tested positive for SARS-CoV-2 divided by the total number of persons tested for a given case finding strategy during the study period. For inferential statistics, we analyzed the overall positivity over the entire period from April to Mid-August 2020 because some case finding strategies had no results or very low number of tests to have a valid comparison.

 

Multivariable logistic regression was used to assess the association between age, sex, geography (province), and case finding strategy with SARS-CoV-2 test positivity. We reported the odds ratios (OR) and 95% confidence intervals (CIs). Statistical significance was set at a p-value ≤0.05. STATA version 15.1 (College Station, USA) was used for statistical analysis.

 

Ethical approval to conduct this study was granted by the national health research authority.

 

 

A total of 100,584 case records had SARS-CoV-2 PCR tests results with 8,992 (8.9%) confirmed SARS-CoV-2 positive. Only 3,686 (41.0%) of the positive cases were linked to a case finding strategy.

 

Out of the 100,584 cases, only 27,453 (27.3%) persons had a case finding strategy listed with their test result. Among these 3,686 (13.4%) were confirmed SARS-CoV-2 positive Table 1.

 

The mean age for positive SARS-CoV-2 persons was 35 years (SD:17.2), males represented 58.6%. The highest number of SARS-CoV-2 cases were observed from Lusaka district 1059 (28.7%), Ndola district 625 (16.9%), Kitwe district 175 (4.7%), Chililabombwe district 163 (4.4%), Kabwe district 145 (3.9%) and Solwezi 140 (3.8%). The remaining districts had less than 100 cases each Table 2.

 

Overall test positivity in Zambia among those with a known case finding strategy during the study period was 13.4% (3686/27,453). The positivity rate increased from 1.1% in April to 27.3% by August 13 among those with a known case finding strategy Table 3. The positivity for health facility testing increased from 6.9% in May to 30.7% in August. Among the contacts, the positivity rate increased from 2.4% to in April to 21.9% in August. For community alerts the positivity increased from 1.8% in April to 33.8% in August. For special operations and points of entry the positivity increased from 0.7% and 3.1% in April to 22.0% and 20.9% in August respectively.

 

The adjusted odds of testing positive for SARS-CoV-2 were highest for health facility testing (OR 13.3, 95% CI: 11.5-15.3; p-value-0.001) and lowest for points of entry (OR 3.32, 95% CI:2.63-4.18, p=0.001) compared to special operations Table 4.

 

There was no statistically significant difference in the odds of testing positive for SARS-CoV-2 between females and males (OR=1.03 {95% CI: 0.98-1.13}; p-value=0.512). The adjusted odds of testing positive for SARS-CoV-2 increased with age; the highest odds observed were among those aged 60-69 years compared to children ≤ 9 years (OR=2.26 {95% CI: 1.73-2.95}; p-value 0.001). North-Western province had highest adjusted odds of having SARS-CoV-2 positives; (OR=4.64 {95% CI: 3.43.-6.28}; p-value=0.001) compared to Lusaka province. While Eastern province had lowest adjusted Odds of having SARS-CoV-2 positives; (OR=0.09 {95% CI: 0.01-0.68}; p-value=0.019) Table 4.

 

 

The overall positivity rate for SARS-CoV-2 in Zambia increased from 0.6% in April to 8.9% during mid-August. This is likely attributable to increased community transmission, as percent positivity has been shown to correspond with SARS-CoV-2 transmission especially in setting where testing is limited (as in Zambia) [5]. These findings are consistent with the experience on the ground in Zambia during this time, during which hospitals were strained with patients with COVID like symptoms.

 

SARS-CoV-2 test positivity varied among the different case finding strategies in Zambia during the study period. Test positivity in the month of April was highest for the travellers entering the nation. However, test positivity in the travellers declined in May, dropped to zero in June and then increased in July and August, a pattern that is potentially consistent with seeding from international traveller and subsequent local transmission. However, this decline could also be attributed to reduction in testing of travellers because of travel restrictions. The lowest positivity rate in April and May was observed among tests conducted during special operations (0.7% April, 1.1% June). The possible reasons for this low positivity is probably because of the non-specific nature of this testing strategy. However, given the high number of tests done via this case finding strategy more positives were found at a given time using this strategy than other strategies.

 

In May, the highest positivity rate was observed among the health facility alerts (6.9%). There was an increase in out-patient department (OPD) and inpatient department (IPD) alerts from May 2020. The reduction in community alerts may have been caused by an increased turnaround time for the results, with subsequent declined demand for testing in the community. The increased OPD and IPD alerts was caused by a policy change which directed the health facilities to widen their testing among the OPD and IPD attendees. The higher positivity rates among OPD and IPD indicates this policy directive resulted in an effective case finding strategy.

 

In June, the positivity for SARS-CoV-2 was highest for the contacts 15.6%. This corresponds to a period during the outbreak when cases were still sporadic and rapid response teams (RRTs) had been activated throughout the nation. It is possible that RRTs were at their maximum effectiveness during this period before community transmission began and contact tracing became less feasible, in Zambia.

 

We observed an upsurge of SARS-CoV-2 cases in July from all the case finding strategies except community alerts. This could be attributed to reduced testing from community alerts. The highest positivity was observed for health facility testing and lowest for the travellers. In August, the same trend continued with community alerts yielding the highest positivity rate. Such high percent positivity was clear indication of community transmission.

 

The adjusted odds of testing were highest among those persons tested at health facilities and community alerts compared to mass testing of community members and travellers without signs and symptoms suggestive of SARS-CoV-2. For a resource limited country like Zambia, targeted testing is encouraged in order to identify patients who maybe at a higher risk of developing complications of SARs-CoV-2 and mortality than asymptomatic individuals who may not need any medical attention.

 

There was no difference in terms of odds of testing positive between children less than 10 years and children 10-19 years of age. From age 20 years the odds of being SARS-CoV-2 case increased with age group with the highest observed among those aged 60-69 years. Children likely have lower risk of infection with SAR-CoV-2; surveillance reports in the U.S.A found lower incidence among those below the age of 10, representing 1.5% of the total confirmed SARS-CoV-2 cases [6,7]. While children appear to have lower risk of SARS-CoV-2, the lower positivity rate among children could also result from lower testing among this group as well as quality of the specimen collected which requires addition skills and techniques to improve the positivity rate. The other reason could be because children have reduced outdoor activities since schools were closed during the study period. However, this may not be true for certain areas such as the unplanned settlements and rural areas where the restrictions could have not been implemented accordingly.

 

This study has some limitations. Only persons who had information on case finding strategy were included in the analysis, which was a minority of persons, particularly in June. Even when case finding strategy was available there were a lot of missing information (e.g., relationship to contacts and age). These findings are not representative of the entire Zambia and not generalizable to other countries. Testing on community deaths, which was another surveillance strategy in Zambia was not included in the analysis, because the data was not captured electronically compared to other case finding strategy. However, a separate study was conducted to measure the excess mortality due to SARS-COv-2 which is still ongoing. Zambia started implementing the COVID-19 DHIS2 tracker in October of 2020 aimed at addressing the COVID-19 data quality.

 

 

This data indicated increased community transmission of SARS-CoV-2 in Zambia Case finding strategies varied in the positivity rates, and given testing shortages, Zambia might consider prioritizing higher efficiency case finding strategies like contact tracing as well as community and health facility alerts. As the epidemic evolves, continuous analysis of case finding data will enable improved characterization of the epidemic in Zambia as well as help ensure efficient use of resources. There is need to improve the data capturing to improve the data quality for the results to be generalized to the wide population. Zambia started the implementation of the COVID-19 DHIS2 tracker to improve the COVID-19 data quality.

 

 

The authors have declared no competing interests.

 

 

Banda Dabwitso Jezreel, Warren Malambo, Jonas Zajac Hines, Ernest Kateule and Nyambe Sinyange developed the concept and study protocol, participated in data collection and manuscript writing. Banda Dabwitso J, Warren Malambo and Jonas Zajac Hines conducted the data analysis and interpretations. Muzala Kapina and Nyambe Sinyange authorized the final version of the manuscript for publication.

 

 

We would like to acknowledge the support of the Zambia National Public Health Institute and Centers for Diseases Control and Prevention during the entire process of the study from proposal development to manuscript writing.

 

 

Table 1: Sample size metrics for SARS-CoV-2 case finding strategies, April-August 2020.

Table 2: Average Positivity Rates among Contacts, Health facility testing, Community alerts, Points of entry and Special operation, Zambia, April to August, 2020

Table 3: Adjusted Odds Ratios for being a SARS-CoV-2 Cases Among Case Finding Strategies, Zambia April to August, 2020

Table 4: Adjusted Odds Ratios for being a SARS-CoV-2 Cases Among Case Finding Strategies, Zambia April to August, 2020

 

 

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