BACKGROUND
1. Lassa Fever (LF) is an acute viral haemorrhagic fever (VHF) caused by the Lassa virus, which is known to be endemic in parts of West Africa including Benin, Ghana, Guinea, Liberia, Mali, Nigeria and Sierra Leone, but likely exists in other West African countries.
TRANSMISSION
2. Lassa virus is an arenavirus and its natural reservoir is the Mastomys natalensis multi-mammate rat (not native outside Africa) and contact with infected rodents or their excreta remains the key route of human infection.
3. Human-to-human transmission can occur through direct exposure to blood or other bodily fluids from an infected person. The incubation period of the disease ranges from 2 to 21 days (average 10 days). The overall case-fatality rate for LF is around 1 to 2% in Africa but can reach up to 20% in severe hospitalised cases.
4. In the endemic countries, LF cases typically peak during the dry season from November to May. However, transmission also occurs all year round with sporadic cases being reported, but below epidemic thresholds. About 100,000-300,000 cases occur per year in West Africa, with an estimated 5,000 deaths/year.
RISK OF EXPOSURE
5. The risk of importation of a LF case into Singapore is considered very low due to the very low travel volume between the affected countries in West Africa and Singapore.
6. The likelihood of exposure to LF during travel may increase during seasonal flare-ups in affected countries, but largely limited to visitors to rural areas, where living conditions are basic and the likelihood of entering into contact with infected rodents or their excreta is high. This risk of infection can be significantly reduced if travellers are informed and aware of the risks, particularly in areas with ongoing transmission.
7. In the event of an importation, prompt recognition of suspected cases and meticulous infection control practices in healthcare institutions will mitigate the risks and prevent onward transmission.
SYMPTOMS
8. Infection is mild in 80% of cases (low grade fever, malaise, headache). In 20% of patients, more prominent symptoms and severe disease may develop. These include pharyngitis, respiratory and gastrointestinal symptoms, conjunctivitis, abdominal/chest/back pain, and in severe cases facial swelling, bleeding, shock, encephalitis, pulmonary oedema, multi-organ failure. Incubation period of the disease ranges from 2 to 21 days (average 10 days).
9. As the signs and symptoms for LF are varied and non-specific, doctors should be alert to any traveller from LF-affected regions with a febrile illness and should always ask for a travel history.
10. All suspected cases meeting the case definition below should be identified for LF investigation:
AND
Onset of symptoms within 21 days of:
i. travel history to an endemic area (West Africa, mainly in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, and Nigeria); OR
ii. travel history to an area with an ongoing LF outbreak, OR
iii. contact with a patient with suspect or confirmed LF.
11. Suspect cases should immediately be notified to the Ministry of Health (MOH). MOH will arrange for transfer of suspected cases to the National Centre for Infectious Diseases (NCID) on a case-by-case basis. All confirmed LF cases will be managed at the High-Level Isolation Unit (HLIU) in NCID.
DIAGNOSIS
12. Clinical diagnosis of LF is often difficult because the symptoms of LF are varied and non-specific. Diagnosis in acute infection is primarily by detection of Lassa Virus by PCR in blood specimens and/or virus isolation from throat swab or urine specimen. The level of viremia generally declines after the sixth day of illness, but in severe cases may persist till mortality.
13. Diagnostic tests for Lassa virus infections should be performed only after discussion with MOH and the National Public Health Laboratory (NPHL) and samples can be sent to NPHL for diagnosis. The hospital laboratory should contact NPHL for further assistance.
TREATMENT
14. The initial clinical manifestations of LF are non-specific and may be similar to other diseases such as the other VHFs, (e.g., Yellow Fever, Dengue, Ebola/Marburg virus), malaria, rickettsial infections, enteric fever (typhoid and paratyphoid fever) and influenza. Pending diagnostic evaluation for LF and other VHFs, and diagnostic evaluation for other similar illness, empiric treatment (e.g., for malaria, enteric fever, rickettsial disease) should be considered, according to local guidelines.
15. Treatment of LF is supportive care and with ribavirin. Consider early initiation of ribavirin for confirmed cases. Intravenous ribavirin is preferred over oral ribavirin, if available. Ribavirin is teratogenic and careful counselling about side effects and impact on conception plans for six months must be discussed with patients.
16. Patients with confirmed Lassa Fever will be transferred for further management at the HLIU in NCID. Treatment consists of supportive care and IV ribavirin.
INFECTION CONTROL
17. Patients who are under investigation for LF, pending transfer to the HLIU in NCID, should be isolated in a single-bedded isolation room, and be placed on strict contact and respiratory precautions. Entry of non-essential staff to the patient’s room should be restricted, a register of all staff who enter the patient’s room should be maintained and visitors should not be allowed.
18. All staff who come into direct contact with a suspect or confirmed LF case or their body fluids, including (but not limited to) healthcare workers, persons responsible for transporting patients (e.g., ambulance staff), and cleaners should apply extra infection control measures and wear enhanced personal protective equipment (PPE)1.
19. Waste generated from suspect patients should be double bagged, sealed and disposed of by a licensed waste-contractor2.
20. Contacts of persons with LF or healthcare workers with unprotected exposure to an infected patient or their body fluids are at risk of acquiring disease. Such exposures include exposure of mucous membranes or broken skin to blood/body fluids (including respiratory secretions), without the proper PPE, or needle stick injury.
21. In the case of exposure to an infected person, exposed persons should immediately seek advice from an Infectious Diseases physician and report the exposure to MOH. Close contacts will be contact traced by MOH and appropriately followed up (e.g., quarantine, phone surveillance or self-monitoring). Contacts may be referred to NCID for assessment and post-exposure prophylaxis with oral ribavirin.
1 Enhanced PPE is designated for those with direct patient care/contact. Many hospital staff will thus not need to follow the enhanced PPE recommendation. In such cases, hospitals’ own protocol should be followed.
2 Please refer to MOH Circular 35/2019, which contains detailed guidance on PPE use, waste management and the handling of dead bodies (with suspected or confirmed EVD).
