What is the epidemiology of primary amoebic meningoencephalitis (PAM)?

Epidemiology of Primary Amoebic Meningoencephalitis (PAM)

Primary Amoebic Meningoencephalitis (PAM) is a rare but nearly always fatal disease caused by Naegleria fowleri, with cases historically concentrated in southern US states but recently expanding to northern regions, predominantly affecting children and young adults with exposure to warm freshwater. 1, 2

Geographic Distribution and Trends

• PAM has worldwide occurrence but is most frequently reported in warm climate regions 3
• Historically in the US, cases were primarily reported from southern states 1
• Recent expansion to northern US states has been observed, with cases reported in Minnesota, Kansas, and Indiana 4
• PAM is likely underreported globally, with many cases potentially undiagnosed or diagnosed postmortem 5

Demographic Patterns

• Predominantly affects children and young adults, with a median age of 12-14 years in US studies 4, 3
• Males are disproportionately affected, comprising 75-84% of reported cases 4, 3
• In Pakistan, a higher median age of 34 years has been reported, suggesting regional variations in affected populations 6

Exposure Sources and Risk Factors

• Swimming or diving in warm freshwater lakes, ponds, and reservoirs is the most common exposure 2, 3
• Cases occur predominantly during summer months when water temperatures are higher 7
• Nasal irrigation with untreated water (including neti pots) is an emerging risk factor 2
• Ritual nasal ablution practices have been implicated in some regions 2
• Playing on lawn water slides connected to municipal water supplies has been identified as a risk factor 2

Disease Burden and Surveillance

• PAM has an extremely high mortality rate exceeding 95% 2, 7
• Only a small number of survivors have been documented worldwide 4
• Pre-mortem diagnosis is confirmed in only 27% of cases, highlighting diagnostic challenges 4
• Many additional cases likely go unrecognized, as suggested by the high proportion of US PAM cases diagnosed postmortem 1
• Limited surveillance systems and diagnostic capabilities contribute to underreporting 1, 5

Pathogen Exposure and Disease Development

• Exposure to N. fowleri is believed to be common, but disease development is rare 1
• It remains unclear why some exposed individuals develop disease while the majority do not 1
• The amoeba enters the body through the nasal passage during water activities or nasal irrigation 2
• Disease progression is extremely rapid, with death typically occurring within 5 days of symptom onset if untreated 2, 7

Public Health Implications

• Enhanced surveillance and improved diagnostic capabilities are needed to better understand the true burden of PAM 1, 5
• Environmental testing could help delineate reservoirs of disease 1
• Preventive measures include avoiding swimming in warm freshwater, preventing nasal water exposure, and avoiding nasal irrigation with untreated water 7
• Chlorination of recreational water bodies, especially after prolonged periods of non-use, is recommended 8

Clinical Considerations for Early Detection

• PAM should be included in the differential diagnosis for any patient with rapidly progressive meningoencephalitis following water exposure or nasal lavage 2, 7
• Early diagnosis and immediate treatment initiation are critical factors for potential survival 7
• CSF findings resemble bacterial meningitis with high opening pressures, elevated WBC counts (predominantly neutrophils), low glucose, and elevated protein 4, 6