Understanding the causes of pneumonia in refugee populations in Lebanon to improve prevention and treatment.




Middle East








The PEARL study was launched in Lebanon in 2016 to evaluate the proportions and distribution of community-acquired pneumonia attributable to the different viral and bacterial pathogens in refugee and Lebanese populations. The results will provide a factual basis for assessing epidemiological risks, designing public health interventions and determining effective treatment protocols.

Context and scientific objectives

The harsh conditions in refugee camps are accelerating the spread of infectious diseases, particularly pneumonia, the leading infectious cause of child mortality. Community-acquired pneumonia is the most common cause of admission to health centers.

The Mérieux Foundation initiated the PEARL study with local partners to understand the causes of community pneumonia among refugee and Lebanese populations in the Bekaa Valley and Akkar/Tripoli region (main entry points for Syrian refugees).

The study was conducted from 2016 to 2019 with the aim of providing recommendations for disease prevention and patient care to protect this vulnerable population.

Despite growing concerns about the increasing number of cases of respiratory infections in refugee camps, the causes of community-acquired pneumonia among children and adults in humanitarian crises are unknown.

The PEARL study is the first to systematically establish the prevalence and role of pathogenic microorganisms in the respiratory tract during a humanitarian crisis.


  • A prospective, multi-center case-control study with 686 cases and 686 controls in the Bekaa Valley and the Akkar/Tripoli region.
  • Detection of viruses and pathogenic bacteria in nasopharyngeal or sputum specimens, blood and urine samples.
  • Microbiological analysis of samples (molecular typing of viruses by multiplex PCR and next generation sequencing) carried out at the Rodolphe Mérieux Laboratory at Saint-Joseph University in Beirut and in the Lebanese University laboratory in Tripoli.


Viruses responsible for 81% of the total

The PEARL study provides important insights into the agents responsible for mild to moderate lower respiratory tract infections in the Syrian refugee population of all ages.

In this population, which receives care at primary health centers, the majority of cases of pneumonia and other lower respiratory tract infections were relatively minor. Viruses are responsible for the vast majority of these infections, with 81% of cases attributable to exposure to these pathogens.

Vaccination as an effective weapon

Vaccination of this entire population -children and adults- against respiratory pathogens for which a vaccine exists (influenza, Streptococcus pneumoniae, Haemophilus influenzae, Bordetella pertussis) could prevent many infections. Cases could decrease by up to 43% if immunity against these viruses was developed through vaccination.

Over-use of antibiotics

Despite the fact that antibiotics are ineffective against viruses, significant antibiotic consumption has been observed, in up to 32% of the cases. This antibiotic consumption is often ignored or hidden (only 3% of cases reported having recently taken an antibiotic). In this population, strategies to reduce antibiotic prescriptions could therefore be considered.

Another discovery was that the proportion of respiratory infections attributable to each pathogen varies considerably from year to year, depending on the age of the patients and the severity of disease. Therefore, the proportions and distribution of disease-causing pathogens, like those mapped in the PEARL study, will vary depending on the context.


Investigating Pneumonia Etiology Among Refugees and the Lebanese population (PEARL): A study protocol

Thomas Kesteman, Ali Ghassani, Crystel Hajjar, Valentina Picot, Marwan Osman, Zahraa Alnajjar, Florence Komurian-Pradel, Melina Messaoudi, PEARL Study Group, Hicham Ghazi Soulaiman, Philippe Vanhems, Octavio Ramilo, Dolla Karam-Sarkis, Josette Najjar-Pellet, Monzer Hamze, Hubert Endtz.
Gates Open Research 2018, 2:19 (doi: 10.12688/gatesopenres.12811.1)