Haemophilus influenzae

Background

Haemophilus influenzae (H. influenzae) are bacteria commonly carried in the respiratory tract, which can cause acute invasive disease. They are divided into encapsulated and unencapsulated (non-typeable) strains. Encapsulated strains can be classified into six serotypes, from a to f, of which type b (Hib) was most prevalent prior to vaccine introduction. Infection with H. influenzae can cause the following conditions:

  • meningitis
  • septicaemia
  • acute respiratory infections

Less frequent conditions which may be caused by H. influenzae infection include:

  • epiglottitis
  • osteomyelitis
  • septic arthritis

For more information on H. influenzae, visit the NHS inform website.

Guidance

Guidance on Haemophilus influenzae can be found below:

For all infection prevention and control guidance visit the A-Z ​pathogens section of the National Infection and Prevention Control Manual.

Data and surveillance

In 1992, following introduction of the Hib vaccine for young children, the number of H. influenzae type b cases fell dramatically, not only in the vaccinated group but also in older age groups.  Due to reduced carriage of the organism within the respiratory tract of vaccinated children, transmission to the wider community was effectively suppressed. The addition of the Hib booster vaccine in 2006, reduced case numbers further.

In Scotland, typing is conducted on  all cases with positive laboratory reports for H. influenzae, in order that national trends in disease subtypes can be monitored. Further enhanced surveillance is carried out for all H. influenzae cases identified in children under the age of 5 and type b strains across all age groups.

Surveillance update for April to June 2019

Between April and June 2019 (weeks 14 to 26), 17 cases of invasive H. influenzae were reported, taking the total number of cases reported in the first two quarters of 2019 to 40. This is comparable to cumulative case numbers reported over the previous four years which ranged from 42 to 53 cases, as shown in Figure 1.

Of the 40 cases reported so far in 2019:

  • three (7.5%) were aged under five years
  • two (5.0%) were aged between 21 and 40 years
  • 35 (87.5%) were above 40 years of age

Information on clinical presentation was available for all three paediatric (under 16 years old) cases. Two cases presented with bacteraemia, and one case presented with meningitis.

Figure 1 is a line graph showing the cumulative number of Haemophilus influenzae cases reported to Health Protection Scotland per week by year. Each line represents a different year from 2015 to the second quarter of 2019 and all years show a steady increase in cumulative number of cases per week. A similar number of cases were observed in the first two quarters of 2019 as in the corresponding period of 2018.

Of the 40 invasive cases reported so far in 2019:

  • 34 (85.0%) had influenzae isolated from blood
  • four (10.0%) from cerebrospinal fluid
  • two (5.0%) from pleural fluid

One case is known to have died in 2019, which is comparable to the same period over the previous five years (0 to 1 deaths).

Figure 2 demonstrates the epidemiological impact of the Hib vaccine, for those aged under five (routinely vaccinated group) and for all ages (including under fives). Prevalence has shown a corresponding decrease in cases since 1992 and figures have remained relatively stable since 2011.

Figure 2 is a line graph showing the number of invasive Haemophilus influenzae type b disease cases reported to Health Protection Scotland from 1988 to the second quarter of 2019. There are two lines on the graph, one representing the under 5 age group and the other, total number of cases (including under 5 years). Following introduction of the Hib vaccine in 1992, cases rapidly decreased to single figures. However, in 2001 a sharp increase was observed and total number of cases peaked at 31 in 2002, prompting introduction of the Hib booster campaign in June 2003. Cases across all ages subsequently decreased and following introduction of a routine Hib booster in 2006, reached low numbers by 2009. Only one case has been observed in the under 5 age group between 2011 and second quarter of 2019.

Figure 3 presents laboratory reports by serotype, since the introduction of the Hib booster campaign in 2003.

H. influenzae typing was carried out for 29 (72.5%) isolates, of which:

  • 24 (82.8%) were non-typeable (NT)
  • three (10.3%) were type f
  • one (3.4%) was type b
  • one (3.4%) was type a

All three paediatric cases were non-typeable.

​There continues to be a high proportion of non-typeable (NT) isolates, and isolates not sent for typing.

Figure 3 is a bar chart showing the laboratory reports of Haemophilus influenzae by type from 2003 to the second quarter of 2019. The chart shows a steady decline in type b infection since introduction of the Hib vaccine in 2003, with a corresponding increase in non-typeable strains. Non-typeable strains are now the most commonly reported type, with very few reports of types a, d, e and f.

Vaccine uptake statistics

Vaccine uptake statistics can be found on the Information Services Division (ISD) website.