Middle East respiratory syndrome #coronavirus {#MERS-CoV} - Kingdom of #Saudi Arabia (#WHO D.O.N., May 12 '25)

Situation at a glance

Between 1 March and 21 April 2025, the Ministry of Health (MoH) of the Kingdom of Saudi Arabia (KSA) reported nine cases of Middle East respiratory syndrome coronavirus (MERS-CoV) infection. Two of these cases died. Among the nine cases, a cluster of seven cases were identified in Riyadh, including six health and care workers who acquired the infection from caring for a single infected patient. The cluster was identified through contact tracing and subsequent testing of all contacts, with four of the six health and care workers being asymptomatic and two showing only mild, nonspecific signs. The notification of these cases does not change the overall risk assessment, which remains moderate at both the global and regional levels. These cases show that the virus continues to pose a threat in countries where it is circulating in dromedary camels and spilling over into the human population. WHO recommends implementation of targeted infection prevention and control (IPC) measures to prevent the spread of health-care-associated infections of MERS-CoV and onward human transmission.

Description of the situation

Between 1 March and 21 April 2025, the Ministry of Health (MoH) of the Kingdom of Saudi Arabia (KSA) reported nine cases of MERS-CoV infection. 

The cases were reported from the Hail (1) and Riyadh (8) regions of Saudi Arabia (Figure 1). Of the reported cases, five were male and four were female.

Among these cases, a cluster of seven was identified in Riyadh, including six health and care workers who acquired a nosocomial infection from one single infected patient they had cared for. 

Of the six health and care workers, four remained asymptomatic, while two developed mild, nonspecific symptoms including myalgia, fatigue, nausea and vomiting (...). 

Laboratory confirmation of the cases was performed by real-time polymerase chain reaction (RT-PCR) between 1 March 2025 and 16 April 2025. 

Of the cases, only one had indirect contact with camels and is not a part of the reported cluster. The rest of the patients had no known history of contact with camels or camel products.

Since the first report of MERS-CoV in KSA in 2012, a total 2627 laboratory-confirmed cases of MERS-CoV infection, with 946 associated deaths (Case Fatality Rate or CFR of 36%), have been reported to WHO from 27 countries, across all six WHO regions. 

The majority of cases (2218; 84%), have been reported from KSA, including these newly reported cases (...). Since 2019, no human MERS-CoV infections have been reported from countries outside the Middle East.

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Epidemiology

Middle East respiratory syndrome (MERS) is a respiratory illness caused by a coronavirus (MERS-CoV). The fatality rate among confirmed cases is around 36%, though this may be an overestimate since milder cases often go undetected. The CFR is calculated based solely on laboratory-confirmed infections, which may not reflect the correct mortality rate.

Humans contract MERS-CoV through direct or indirect contact with dromedary camels, the virus’s natural host and zoonotic reservoir. 

Human-to-human transmission occurs via infectious respiratory particles mainly at close distances and also through contact transmission, it has mainly occurred in close-contact situations, particularly in health-care settings. 

Outside these environments, there has been limited documented human-to-human transmission to date. 

MERS can present with no symptoms, mild respiratory issues, or severe illness leading to acute respiratory distress and death. 

Common symptoms include fever, cough, and breathing difficulties, with pneumonia frequently observed, though not always present. 

Some patients also experience gastrointestinal symptoms such as diarrhoea. 

Severe cases may require intensive care, including mechanical ventilation. Those at higher risk of severe outcomes include older adults, individuals with weakened immune systems, and those with chronic conditions like diabetes, kidney disease, cancer, or lung disorders.

The number of MERS-CoV infections reported to WHO has substantially declined since the beginning of the COVID-19 pandemic. 

Initially, this was likely the result of epidemiological surveillance for SARS-CoV-2 being prioritized. 

The similar clinical picture of both diseases may result in reduced testing and detection of MERS-CoV infections. 

However, the Ministry of Health of KSA has been working to improve testing capacities for better detection of MERS-CoV since the easing of the COVID-19 pandemic, with MERS-CoV included into sentinel surveillance testing algorithms since the second quarter of 2023, for samples that test negative for both influenza and SARS-CoV-2. 

In addition, measures taken to reduce SARS-CoV-2 transmission (e.g., IPC measures such as mask-wearing, hand hygiene, physical distancing, improving the ventilation of indoor spaces, respiratory etiquette, stay-at-home orders, reduced mobility) also likely reduced opportunities for onward human-to-human transmission of MERS-CoV. 

Potential cross-protection conferred from infection with or vaccination against SARS-CoV-2 and any reduction in MERS-CoV infection or disease severity and vice versa has been hypothesized but requires further investigation.

No vaccine or specific treatment is currently available, although several MERS-CoV-specific vaccines and therapeutics are in development. Treatment remains supportive, focusing on managing symptoms based on the severity of the illness.

Public health response

The Ministry of Health of KSA implemented the following response measures

-- Infection prevention and control (IPC) measures in healthcare settings:

- Regular training of health and care workers on IPC measures.

- Implementation of stringent IPC measures, including triage protocols, use of personal protective equipment (PPE), and isolation procedures for suspected cases.

- Prompt isolation of cases and quarantine of contacts.

-- Surveillance and testing:

- Rigorous contact tracing and testing of high-risk contacts, including healthcare workers.

- Inclusion of MERS-CoV in sentinel surveillance testing algorithms since 2023.

-- Public health awareness and hygiene practices:

- Public health awareness campaigns to prevent human-to-human transmission.

- Advising people with underlying chronic medical conditions to avoid close contact with animals, particularly dromedaries.

WHO risk assessment

As of 21 April 2025, a total of 2627 laboratory-confirmed cases of MERS-CoV infection have been reported globally to the WHO, with 946 associated deaths. 

The majority of these cases have occurred in countries within the Arabian Peninsula, with 2218 cases (84.4%) and 865 related deaths (CFR 39%) reported from the KSA. 

A notable outbreak outside the Middle East occurred in the Republic of Korea, in May 2015, during which 186 laboratory-confirmed cases (185 in the Republic of Korea and 1 in China) and 38 deaths were reported. However, the index case in that outbreak had a travel history to the Middle East. 

The global case count reflects laboratory-confirmed cases reported to WHO under IHR (2005) or directly by Ministries of Health to date. These numbers may underestimate the true number of cases if some were not reported. The total number of deaths includes those that WHO has been officially informed of, based on follow-up with affected Member States. 

Humans are infected with MERS-CoV from direct or indirect contact with dromedaries who are the natural host and zoonotic source of the MERS-CoV infection. MERS-CoV has demonstrated the ability to be transmitted between humans. 

So far, the observed non-sustained human-to-human transmission has occurred among close contacts and in health care settings. Outside of the healthcare setting there has been limited human-to human transmission.  

The notification of these cases does not change the overall risk assessment. The reported cluster of six secondary cases among health and care workers is the result of rigorous contact tracing and testing performed by KSA, with four of the six cases being asymptomatic and two showing only mild, unspecific signs. 

WHO expects that additional cases of MERS-CoV infection will be reported from the Middle East and/or other countries where MERS-CoV is circulating in dromedaries, and that cases will continue to be exported to other countries by individuals who were exposed to the virus through contact with dromedaries or their products (for example, consumption of raw camel milk), or in a healthcare setting. 

WHO continues to monitor the epidemiological situation and conducts risk assessment based on the latest available information.  

WHO advice

Based on the current situation and available information, WHO reemphasizes the importance of strong surveillance by all Member States for acute respiratory infections, including MERS-CoV where warranted, and to carefully review any unusual patterns. 

Delays in recognizing the early symptoms of MERS-CoV infection, slow triage of suspected cases and delays in implementing IPC measures have been linked with human-to-human transmission of MERS-CoV in health-care settings in past outbreaks. IPC measures are therefore critical to prevent the spread of healthcare-associated infections of MERS-CoV. Health and care workers should always apply standard precautions consistently with all patients, at every interaction in healthcare settings.

Ventilation rates in general patient care rooms should meet or exceed 60 litres per second per patient (or 6 air changes per hour). 

In addition, contact and droplet precautions, which include patient placement in single rooms with dedicated care equipment, and the use of personal protective equipment (PPE) such as clean non-sterile gown, gloves, eye protection and a well-fitting medical mask, should be added to standard precautions when providing care to patients with suspected or confirmed MERS-CoV. 

Airborne precautions should be added when performing aerosol-generating procedures or in settings where aerosol-generating procedures are conducted, including the use of procedure rooms with ventilation rates meeting or exceeding 160 litres per second (or 12 air changes per hour). 

Early identification, case management and prompt isolation of cases, quarantine of contacts, together with appropriate IPC measures in health care settings and public health awareness can prevent human-to-human transmission of MERS-CoV. 

MERS-CoV appears to cause more severe disease in people with underlying chronic medical conditions such as diabetes, renal failure, chronic lung disease, and immunocompromised persons. Therefore, people with these underlying medical conditions should avoid close contact with animals, particularly dromedaries, when visiting farms, markets, or barn areas where the virus may be circulating.

General hygiene measures, such as regular hand washing before and after touching animals and avoiding contact with sick animals, should be adhered to. 

In addition to contact with animals, hygiene practices should be observed when dealing with food items of camels; people should avoid drinking raw camel milk or camel urine or eating meat that has not been properly cooked. 

WHO does not advise special screening at points of entry with regard to this event, nor does it currently recommend the application of any travel or trade restrictions.

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Citable reference: World Health Organization (12 May 2025). Disease Outbreak News; Middle East Respiratory Syndrome coronavirus – Kingdom of Saudi Arabia. Available at: https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON569

Source: World Health Organization, https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON569

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