Target product profiles for diagnosis of sepsis: Proposing a new approach for diagnostic innovation

Sepsis is a life threatening condition due to a dysregulated host response to infection1,2 and is associated with high morbidity and mortality in hospitalized patients3, especially in intensive care units4. In 2017, 48.9 million sepsis cases were recorded globally resulting in 19.7 per cent of all global deaths5. Incidence of reported sepsis is maximum in neonates affecting nearly three million babies globally with 11-19 per cent mortality6,7. Its burden remains highest in low- and middle-income countries (LMICs) of Asia and sub-Saharan Africa3,5. The data on sepsis epidemiology of India remain inadequate because of sparse surveillance and lack of appropriate diagnostic tools8,9. Gram-negative pathogens Klebsiella spp., Acinetobacter spp. and Escherichia coli have been reported as predominant causes of neonatal sepsis in Indian tertiary care hospitals8,9. Sepsis in adults is associated with high rates of antimicrobial resistance (AMR) and high mortality rates in Indian hospitals10.

Early treatment decisions supported by the right diagnosis can substantially improve outcomes in sepsis patients. Blood culture remains only accepted method to diagnose pathogens causing sepsis and determine their antimicrobial susceptibility profile11,12. Due to low sensitivity, about 40 per cent of the patients with sepsis are missed by blood culture13-15 and long turnaround time (TAT) of 48-72 h negatively impacts patient management decisions, especially in neonates, resulting in poor survival16.

Many culture-independent techniques with fast TAT have now become available, but sub-optimal sensitivity and prohibitively high cost restrict their clinical usefulness17-20. Biomarker-based tests have shown a role in sepsis diagnosis, prognosis and therapeutics21, but their use in routine practice is limited due to lack of acceptable specificity/sensitivity criteria22-24. Accurate and affordable rapid diagnostics are therefore urgently needed in this context.

At present, no target product profile (TPP) or guidance document exists that can be used as a reference for developing rapid diagnostics for sepsis/neonatal sepsis. A few guiding documents on simplified blood culture system25 and empirical treatment of neonatal sepsis26-28, although available, do little to address diagnostic needs. This manuscript presents TPPs for rapid diagnostics to facilitate early detection of sepsis/neonatal sepsis and to serve as a reference point for stakeholders interested in developing new diagnostics. These TPPs have been specifically aligned to Indian healthcare settings and can also be extrapolated to other resource-constraint and high disease burden settings.

Material & Methods

Study design: This was a qualitative study that followed a consultative process of Delphi surveys to draft TPPs. The guiding principles were affordability of end-products and usability in Indian health systems. A working group comprising experts drawing on in-country knowledge and practice of medicine was constituted to steer the process. The study did not involve any human and/or animal specimens. The study design and protocol was approved by the Indian Council of Medical Research (ICMR), New Delhi.

Working group: The ICMR constituted a task force to facilitate development of rapid tests for pathogen detection and/or antimicrobial susceptibility testing. This task force works with a ‘Technical Advisory Group on AMR Diagnostics’ (TAG-Dx), a seven-member expert committee of clinicians, paediatricians, microbiologists, researchers, public health specialists and representative of the national programme. A working group comprising task force and TAG-Dx members, identified sepsis and neonatal sepsis as a priority for which quality diagnostics were urgently needed. There were five key steps to developing TPPs:

Review of literature: A structured review of relevant literature related to the burden of sepsis, neonatal sepsis, aetiology, diagnosis and cost was undertaken. Key search words used were ‘disease burden’, ‘paediatric’, ‘neonates’, ‘bacteria’, ‘viral pathogen’, ‘sepsis’, ‘aetiology’, ‘diagnosis’, ‘diagnostic’, ‘tests’, ‘RDTs’, ‘point-of-care’, ‘blood culture’, ‘bloodstream infection’, ‘AMR’, ‘target product profile’, ‘analytical’, ‘operational’, ‘characteristics’ and ‘India’. Published TPPs for diagnosis of other syndromes such as tuberculosis, gonorrhoea and HIV and on guidance for antimicrobial therapy were consulted25,27,28.

Identifying stakeholders: A list of 50 potential stakeholders was identified to constitute an expert panel for the Delphi survey. The chosen stakeholders represented (i) national disease control programmes; (ii) Clinicians, microbiologists from government and private hospitals and NGOs; (iii) engineering and biology researchers from scientific and technical institutes/organizations; (iv) international organizations and global health experts and (v) industry [pharmaceutical and in vitro diagnostics (IVD) manufacturers]. This study did not engage the public and/or patients at any stage of TPP development.

Defining key target product profile (TPP) domains: The key characteristics of TPPs for which test requirements needed to be defined fell under three domains, i.e. (i) scope of test, (ii) performance, and (iii) operational characteristics (Fig. 1). Each characteristic was defined to have ‘minimal requirements’ that a test must possess and ‘optimal requirements’ representing desirable attributes sought to fulfil healthcare requirements. Draft TPPs stating the document purpose and covering all minimal and optimal requirements for characteristics were developed for rapid diagnostics for sepsis and neonatal sepsis.

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Fig. 1

Characteristics of Target Product profiles (TPPs).

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Delphi method: A three-round Delphi method, including two online surveys and one virtual consultation, was adopted to build consensus on TPP characteristics (Fig. 2). A panel of 23 experts with relevant regional, national and international expertise was constituted for online Delphi surveys. Experts were from the fields of public health (national = 2; global = 2), microbiology (n=6), virology (n=2), clinical practice (n=6), research scientists (n=3) and technology experts/innovators (n=2) (Fig. 3).

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Fig. 2

Process flow of Delphi survey to develop and finalize the TPPs. TPPs, target product profiles; AMR, antimicrobial resistance.

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Fig. 3

Expertise profile of the participants in Delphi panel (n=23).

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Draft TPPs with evaluation pro forma were sent electronically to the Delphi panel. Experts were asked to rank their decisions as agreement or disagreement for each characteristic. Comments and suggestions pertinent to response were invited to guide the discussions. Experts were encouraged to provide inputs on all scopes of test and performance characteristics. Responses were collated and disagreements/concerns of each respondent were discussed in a virtual meeting of the working group. Revised second TPP drafts were sent electronically for the second Delphi round, and the process was again repeated. Consensus agreement was evaluated at ≥50 per cent and ≥85 per cent of responders agreeing with the proposed characteristics.

Final consensus meeting: Experts from the national health programmes, research scientists, clinicians, microbiologists and technology experts were invited for a consensus meeting as part of the third Delphi round. A consultation with working group and subject experts (n=6) was held virtually (September 2021) to discuss suggestions and disagreements. After the closure of Delphi, TPP drafts underwent final revision based on comprehensive stakeholders’ opinion led by the working group. Supporting remarks were provided for each revision in TPP characteristics and revised versions of TPPs were shared with working group for final review.

Results

Primary observations and debates: The comprehensive first drafts of TPPs for sepsis and neonatal sepsis were curated to guide the development of an ideal test for the detection and characterization of causative pathogens. Characteristics (n=38) were prioritized as critical, high, medium and low priority (Supplementary Table I) and categorized in scope of test and performance characteristics (n=9) and operational characteristics (n=29) (Fig. 1). The goal of test included rapid confirmation of sepsis/neonatal sepsis and its differentiation from septic shock, pathogen identification, susceptibility profiling and detection of genetic markers.

A response rate of 73.9 per cent (17/23) was received on first drafts in the first Delphi round (initiated in June 2020) (Fig. 4A). Consensus agreement could not be estimated in this round owing to diverse suggestions on TPP characteristics. Most comments were received on goal, level of healthcare, target user, analytical sensitivity, limit of detection (LoD), specificity, diagnostic sensitivity, target analyte(s), panels for pathogen identification, susceptibility testing and resistance markers. These comments/suggestions were discussed with the working group. The group suggested developing three separate TPPs for screening of sepsis, pathogen identification and testing antimicrobial susceptibility/resistance markers to appropriately address the needs of healthcare providers at different healthcare levels. Second TPP drafts had following three categories for rapid diagnostics for both sepsis and neonatal sepsis: (i) TPP I: Screening of sepsis with high sensitivity (biomarker-based tests); (ii) TPP II: Detection of aetiological agent causing sepsis (bacterial, viral and fungal); (iii) TPP III: Antimicrobial susceptibility/resistance profiling of pathogens causing sepsis.

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Fig. 4

Expertise profile of respondents in Delphi, (A) survey round 1, and (B) survey round 2.

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Minimal and optimal criteria were defined as per TPP modality and its goal. To strengthen flexi-test development, diagnostics based on TPP I and II can be developed independently or into one test/system. Diagnostics based on TPP III can be developed independently of I and II or together with TPP II as one test/system.

In the second Delphi round (initiated in April 2021), a response rate of 69.6 per cent (16/23) was obtained on second drafts (Fig. 4B). For sepsis, a consensus agreement of ≥85 per cent and >50 per cent on TPP criteria was achieved for 21/29 (72%) and 26/29 (89%) of characteristics, respectively. A consensus agreement of ≥85 per cent and 50 per cent was achieved for 25/29 (86%) and 27/29 (93%) characteristics, respectively, for neonatal sepsis. Eighty-five per cent agreement was observed amongst respondents on scope and performance characteristics. Comments/suggestions were primarily on the target level of healthcare, target analyte, sample type and assay type. A high degree of agreement was observed for optimal criteria of TPPs whereas minimal criteria invited maximum differences in opinions.

The working group and experts met virtually (due to the COVID-19 pandemic) for the third Delphi round. An additional characteristic on ‘software/guideline update’ was added to both TPP II and III making a total of 39 characteristics. Consensus TPPs enlisting minimal and optimal criteria for rapid diagnostics for the diagnosis of sepsis (Supplementary Table II) and neonatal sepsis (Supplementary Table III) were finalized.

Salient features of target product profiles (TPPs):

• (i) TPP I emphasizes on using highly specific marker or combination(s) of biomarkers to enable high sensitivity of diagnostic test. Such diagnostics can efficiently differentiate sepsis from non-sepsis by limiting the detection of false positives.

• (ii) Blood culture, despite its limitations, remains the reference of choice owing to its common use in data reporting in India and non-availability of other validated reference(s). For TPP I, gold standard suggested is appropriate available reference for the proposed maker(s) or positive for biomarker along with blood culture.

• (iii) TPP II includes a panel of priority pathogens as per clinical relevance, where pathogen identification up to the species level has been kept desirable, especially for bacterial identification to address cross-recognition within species, for example, Streptococcus spp.

• (iv) Salmonella is included in the pathogen panel because of its frequent occurrence in large number of cases reported from the community and propensity for misdiagnosis. Streptococcus species is also included owing to its importance in Indian community settings.

• (v) For neonatal sepsis, panel includes fungal, for example, Candida spp., and viral pathogens, for example, HSV and Enterovirus, along with bacterial pathogens, which are frequently reported in neonates as a cause of sepsis8,9.

• (vi) Assay type has been kept qualitative and output as binary to avoid user bias in interpretation of results and diagnosis. The range of storage conditions of test kits and shelf-life has been defined as per variable Indian climatic conditions.

• (vii) Capillary or venous blood based on TPP modalities is recommended sample type as it may be challenging to obtain appropriate salivary samples in neonates depending upon the stage of sepsis and to facilitate the development of a highly sensitive test.

• (viii) Sub-district hospital (SDH) and district hospital (DH) or above are recommended levels of healthcare.

Discussion

India continues to have high mortality due to sepsis both in adults and neonates7-10. Timely detection of infection in sepsis patients is a diagnostic dilemma. Affordable rapid diagnostics have the potential to transform sepsis management to save lives. Many rapid diagnostics for the detection of sepsis are available in Indian markets at prohibitively high costs. Despite the presence of prolific innovation sector in India, few indigenously developed diagnostics are finding place in the Indian healthcare system29. TPPs can channelize the investments towards developing ‘fit-for-use’ rapid diagnostics.

In the tiered healthcare system of India, primary health centres (PHCs) or health and wellness centres (HWCs) are first point-of-contact of patients, and placing screening tests such as biomarker-based rapid test at this level can reduce time to detection. However, these centres are not yet equipped to take care of patients with sepsis, and undertaking sepsis test in the absence of a suitable physician/paediatrician will lead to delays in patient referral to the nearest secondary/tertiary care hospitals. Anticipating such situations, which may lead to patient mismanagement, TPPs do not recommend placing sepsis diagnostic at PHCs/HWCs30. As per the National Essential Diagnostic List (NEDL) and Indian Public Health Standards (IPHS), microbiology laboratories and microbiologists are available at the secondary level, i.e. DH and above. Both SDH and DH have paediatricians, physicians and newborn stabilization units31,32, which can treat sepsis patients. Hence, TPPs suggest placing sepsis tests for pathogen identification and susceptibility testing at secondary and above levels.

Test developers are encouraged to report performance measures such as essential agreement, categorical agreement and error rates in addition to sensitivity and specificity for rapid diagnostics for antimicrobial susceptibility/resistance profiling. Test users must be well trained to accurately read and/or interpret test output. Sensitization of end-users such as clinicians on test diagnosis is recommended before its use. The group had different perspectives on assay type, sample type, reference method to be used and target level of healthcare. For biomarker-based tests (TPP I), there was a disagreement (31%; n=5/16) on optimal criteria for assay type where experts were divided between semi-quantitative or quantitative assay format to provide clinical evidence for physiological differences leading to biomarker deregulation and correlation with disease severity. Others (11/16) supported qualitative format to keep test simple and nullifying user bias in interpretation and diagnosis.

Strengths of this work are (i) a step-wise rigorous process to develop consensus-based TPPs; (ii) inclusion of a wide group of stakeholders that brought clarity on local needs and in-country knowledge to capture diverse voices from the field; (iii) in-depth discussions with experts helped in elucidating trade-offs between characteristics and (iv) confidence in robustness of the TPPs. These TPPs can also be adapted by other LMICs in the current form or with modifications as appropriate, based on sepsis aetiology and healthcare structure in the respective countries.

Current TPPs have the following limitations. Viruses or fungi have not been included in the panel of priority pathogens of sepsis TPP (Supplementary Table II; TPP.S.II) in view of the low incidence in Indian patients based on published data from Indian settings8,9,33 and on suggestions of Delphi experts. A TPP detailing minimal and optimal criteria for rapid test targeting fungal pathogens causing sepsis in adults therefore needs to be developed separately. No consensus could be achieved on limit of detection criteria and diagnostic specificity of TPP II and III. Considering the complexity of sepsis management, no patient or public involvement was attempted. These TPPs do not include specifications on regulatory aspects as they fall under the aegis of the Central Drugs Standard Control Organisation in India.

Future directions: This is the first version of TPPs that will continue to evolve as knowledge continues to advance in the context of sepsis and other diseases. Flexi-format diagnostics performing pathogen identification, susceptibility and/or resistance profiling for sepsis are imperative to overcome obstacles of resource-limited healthcare settings. Innovators should be encouraged to develop easy-to-use and cost-effective lateral-flow assays which can be scaled up rapidly in any healthcare setting. Earlier, it would have not been feasible to carry out polymerase chain reaction (PCR) in district-level laboratories in India; however, the COVID-19 outbreak has better prepared the healthcare for molecular-based diagnostics. For example, reverse transcription-PCR is now well established in most of the districts. There is also an urgent need to create awareness about sepsis diagnosis and management amongst clinicians without which diagnostics even if available may remain underutilized.