Reconnecting patients lost to follow-up with care can prevent new HIV transmissions

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The number of HIV transmissions can be reduced by tracing patients who drop out of HIV care, according to a mathematical model published in the online edition of the Journal of Acquired Immune Deficiency Syndromes. Investigators based the model on data obtained from 1000 people receiving antiretroviral therapy in Malawi. Rapidly re-engaging patients with care services prevented approximately four new infections over five years. It was necessary to trace around 120 patients to prevent one infection, but the investigators think the effort would be worthwhile “since a newly infected patient will need life-long treatment and care costing thousands of dollars, and HIV infection can cut short a patient’s life.”

Antiretroviral therapy that suppresses viral load to undetectable levels in associated with a near-zero risk of HIV transmission. However, many patients drop out of regular care and interrupt their treatment, thus allowing their viral load to rebound, increasing the risk of passing on HIV to sexual partners, as well as the risk of damage to their own immune system and health.

An international team of investigators wanted to see if re-engaging patients who were 'lost to follow-up' would help prevent new HIV infections.


loss to follow up

In a research study, participants who drop out before the end of the study. In routine clinical care, patients who do not attend medical appointments and who cannot be contacted.

mathematical models

A range of complex mathematical techniques which aim to simulate a sequence of likely future events, in order to estimate the impact of a health intervention or the spread of an infection.

retention in care

A patient’s regular and ongoing engagement with medical care at a health care facility. 

immune system

The body's mechanisms for fighting infections and eradicating dysfunctional cells.

They therefore developed a mathematical model based on the observed rate of loss to follow-up and the cumulative viral load of 1000 patients receiving antiretroviral therapy in Malawi.

The model included four scenarios:

  • No patients lost to follow-up.
  • No tracing of patients lost to follow-up.
  • Immediate tracing of patients who missed appointments.
  • Delayed tracing (over six months) of patients dropping out of care.

Overall, 440 people were lost to follow-up at some point over the five years of the study.

Cumulative viral load varied according to retention in care and speed of return to follow-up if care was interrupted.

Patients who remained in continuous care had a cumulative viral load of 3.7 million copies/ml. This compared to 8.6 million copies/ml for patients who dropped out of care and never returned, and 8.0 million copies/ml for patients who returned to care after six or more months. Individuals who were immediately reconnected to care had a cumulative viral load of 7.7 million copies/ml.

Without tracing, 50% of patients returned to care within five years. This increased to 59% with delayed tracing and 68% with immediate tracing.

There were an estimated 33 new infections per 1000 patients over five years if patients remained in continuous care. This increased to 54 onward transmissions per 1000 patients if no attempts were made to trace the patients who dropped out of care.

Immediate tracing prevented 3.6 infections per 1000 patients, whereas delayed tracing prevented 2.5 onward transmissions per 1000 patients.

“This mathematical modelling study based on two ART programmes in Malawi found that tracing patients [lost to follow-up] can slightly reduce transmission from patients who started ART,” comment the authors. “The effect depends on the delay between missed visit and tracing.”

If tracing was immediate, an estimated 116 patients needed to be re-engaged with care to prevent one new infection.

“If one tracing clerk can trace 4-5 missing patients per day, preventing a single transmission would require a 1.5 month workload,” calculate the investigators. “The…workload is reasonable in light of the cost of each infection averted.”

The authors conclude: “tracing patients [lost to follow-up] may efficiently reduce HIV transmission in Malawi and similar settings”. However, they caution that transmissions from patients who drop out of care cannot be prevented by tracing alone. “Interventions to keep patients in care and monitoring of adherence and treatment response accurately are likely to be of greater importance than tracing patients lost to follow-up.”


Estill J et al. Tracing patients lost to follow-up and HIV transmission: mathematical modelling study based on two large ART programmes in Malawi. J Acquir Immune Defic Syndr, online publication ahead of print. DOI: 10.1097/QAI.000000000000075, 2014.

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